KNOW YOUR PLANET EARTH (A comprehensive narration of Earth System Science on the occasion of

centennial celebrations of the Department of Geology, BHU, Varanasi)

Ram S. Sharma FNA, FASc.

Former Professor of Geology at BHU, Varanasi

CONTENTS

PREFACE

Introduction: Why should we know the planet Earth?

Chapter 1: Planet Earth and its Cosmic Cousins

1.0 The solar system

1.1 Early observers

1.2 Origin of planet Earth

1.3 Big Bang theory

1.4 Galaxies

1.5 Formation of Earth and other planets

1.6 Characteristics of each planet

1.7 Sun—the Star of the solar system

1.7.1 Chemical composition of the solar system

1.8 How were all elements of Periodic table formed?

1.9 Asteroid belt

1.9.1 Asteroids

1.9.2 Comets

1.9.3 Meteorites: our cosmic visitors

1.9.4 Meteorite impact

1.10 Moon

Chapter 2: Geosphere, our Deep Earth

2.0 The Earth beneath our feet

2.1 Earthquake reveals Earth’s interior

2.1.1 The Earth’s interior was probed

2.2 Earth’s layers

2.2.1 Crust

2.2.2 Mantle

2.2.3 Core

2.3 Earth’s magnetism

2.4 Sun emits electromagnetic radiations

2.4.1 Solar wind

2.5 Reading Earth’s past in rocks

2.6 Records of Earth’s early history

2.7 Geologic Time

2.8 Sun-Earth-Moon interactions

2.8.1 Earth tides

Chapter 3: Hydrosphere, our Blue Earth

3.1The Oceans

3.1.1 Composition of ocean water

3.1.2 Ocean water layering

3.1.3 Ocean currents

3.1.4 Ocean features

3.2 Plate boundaries

3.2.1 Plate tectonics theory

3.3 Hydrological cycle

Chapter 4: Atmosphere, our Airy Earth

4.1 Introduction—Atmosphere an envelope of gases

4.1.1 Atmospheric pressure

4.1.2 Atmospheric layers

4.2 Weather machine

4.3 Monsoon

4.4 Interaction of atmosphere and ocean

Chapter 5: Biosphere and Earth’s Environment

5.1 The Biosphere

5.2 Earth’s Environment

5.3 Greenhouse gases

5.4 Humans and Environment

5.5 Global warming

5.6 Renewable Energy

5.7 CO2 sequestration and storage

Postscript

References

Every human is born ignorant but without the

knowledge of Earth’s history there cannot be

any sense of a planet or of geologic time

PREFACE

Inspiration to write this compendium for popularizing Earth Sciences aroused subsequent

to my keynote lecture delivered at the beginning of the centennial year 2019 of the department of

Geology, Banaras Hindu University. It is my alma mater and it was here that I had my M.Sc. in

Geology in 1960 and thereafter took up the teaching assignment with a short break (1964-1968)

for research work leading to Ph. D. at the University of Basel, Switzerland. On my return, I

continued teaching along with research and serve my alma mater about 35 years until my

retirement in 1997. I had a great fascination for the subject of geology and had a concern for not

including the subject as part of school education where the students are already engaged with

physics, chemistry, math and biology. The subject is also not included in the syllabi of all newer

universities in India. Earth science is the only science discipline which is introduced to students

late, generally at the graduate level. I seriously felt to inculcate awareness about the environment

in which we live. For this objective, people need to be educated about the Earth science. This

science is not only about the solid Earth or Geosphere but it also includes the oceans

(hydrosphere), and the gas envelope (atmosphere) whose physical and chemical processes

operating at different scales affect the plants, animals and other living organisms, all grouped

under Biosphere. Several volumes on each of these spheres or domains of Earth are available but

they are generally meant for specialists; beginners may be frightened to see these fat books on

individual topics. Earth sciences have now reached a stage where they explained not only what

happened in the geological past and is happening at the present time, but can also predict what

will happen in the future. Hence it is felt that every student should have at least some basic

understanding of the subject of Earth sciences, leaving his/her option for doing the major in one

or more of the science subjects, including the geosciences.

We started knowing the Earth only from 200 B.C., although humans arrived on the Earth

since about 20 lac years (= 2 million years). About 2000 years ago there were only 200 crore or

2 billion (2x109) human beings on the Earth. Now we are about 7.0 billion of which 1.25 billion

(125 crore) people are in India itself. The Earth allowed us to live on it. To sustain ourselves, we

exploit the Earth’s raw materials (coal, iron, oil etc.). We are consuming everything from the

Earth at a fast rate. We have water crisis, 40 nations have acute water shortage. If we make a list

of waste that we produce, it is 2 kg per day per person. Because of our clever technology we are

changing the environment. But we must know that any change in the environment or any

chemical change that influences or destroys one organism may well do similar things to all

organisms. For example, the pesticide D.D.T. used for eliminating malaria by mosquito affected

birds and other species. Hence DDT was banned all over the world. This is because all life has a

genetic code based on the same molecular building blocks. It is, therefore, essential that we must

be Geo-literate, Eco-geoliterate to know the Earth. It is necessary to know how the Earth and its

cousins in space are formed. What the Earth is made of and how old is the Earth? What are the

inaccessible parts below our feet and how the solid, liquid and airy envelopes, respectively

called Geosphere, Hydrosphere and Atmosphere, move over different time scales; what way the

planet Earth is unique, and so on. An improved knowledge of the Earth can help us better

understand events such as earthquakes, volcanoes and tsunamis that are related to plate

movements.

To appreciate all these domains of the Earth, the present compendium divides its theme

in 5 chapters; each is shown to be linked with the other ones. Chapter 1, The Planet Earth and

its Cosmic Cousins, starts with a brief review of what different nationals thought about the

Universe and its stars and planets. Here, the origin of the Earth is described in relation to the

solar system and thereafter in relation to the universe. Also, some salient features about the Earth

and other planets as well as with other cosmic cousins are discussed. Chapter 2, Geosphere, our

Deep Earth, covers all the basic information about the Earth, its different layers, their

composition and their origin. A special feature is the discussion of geological time scale which is

understood in million years and not smaller time units to which a common reader is generally

accustomed to when he reads or hears about social events happening in days, months or years but

never in million years. Chapter 3, Hydrosphere, our Blue Earth, deals with the oceans

(hydrosphere) which constitute about 70% of the Earth’s area. The description is on the ocean

water currents, ocean floor topography and the role of ocean on Weather or Earth’s environment.

Chapter 4, Atmosphere, our Airy Earth, describes all about atmosphere, its layers and about

rain and wind to understand weather. Chapter 5, Biosphere and Earth’s Environment,

discusses the relationship of human and the Earth, or of biotic and abiotic world, global warming

caused by natural causes and human activities. A brief discussion is given on Gaia theory of

Lovelock and to the question of Earth as self regulating system. Suggestions have been offered

for the steps needed to be undertaken by the humans to protect Earth’s environment. The science

contents in the book are written in a style ―as simple as possible but not simpler‖, in the words of

Albert Einstein. This is likely to benefit school-going students and common man in the

enhancement of general understanding of the Earth. To keep the text in a story telling style I

have not included any figure which can be easily conceived by a serious reader.

The book contains only essential information which must be known to a socially

responsible individual and is free of irrelevant material and mathematical equations. A reader by

going through it cover-to-cover is sure to get general understanding of all aspects of the Earth

sciences. My wife, Kanchan, gave me all support in writing this compendium. I am extremely

happy to present this booklet for those who are curious to know the planet Earth, especially at a

time when my alma mater completes its 100 years of imparting knowledge of Earth science to

several thousands of students from India and abroad. Finally, I sincerely thank the Organizing

Committee for the One hundred year Celebration and the Head of the Department, Professor

Rajesh Kumar Srivastava for uploading this compendium as PDF on the Centennial Web page

for the use of any interested individual.

Jaipur, 2019

Ram S. Sharma

sharma.r.sw@gmail.com

INTRODUCTION: Why should we know the planet Earth?

The planet Earth is our home. It behaves as a system in which land (rock), ocean, air and

living organisms interact through physical, chemical and biological processes that move

materials and energy on the Earth. Thus, the Earth system has four domains of study, viz.

Geosphere (from surface to the center of the Earth), Hydrosphere (all water on the Earth),

Atmosphere (blanket of air surrounding the planet) and Biosphere (life and the environment).

These four domains or spheres of study constitute an important branch of natural science, the

Earth System Science. The Earth System Science (ESS) is broadest in scope of natural

sciences. It gives full understanding of the world we live in and also gives full information of

natural resources which sustain the society for its basic requirements. In the ESS we study all

about the Earth and its processes. Everyone is affected by the Earth processes, for example

climate change. In ESS we study how the landscapes formed, where are water and natural

resources now and where would they be in future, where earthquakes or volcanoes can

occur— these and other events of great concern to human society. The Earth System Science

covers five study areas: (1) Geology—physics and chemistry application to the study of

Earth materials and its processes. (2) Astronomy—study of other planes and stars by

application of physics, chemistry and geology. (3) Meteorology—forces and processes in

atmosphere changing weather and affecting Earth’s climate. (4) Oceanography—physical

and chemical properties of ocean and its lives. (5) Environmental science---interaction of

organisms with their surroundings. Study of geology or geosciences has led to many

discoveries and the application of these scientific discoveries is called technology.

Technology gave Geofacts. For example, Earth core is located 6378 km from the surface;

Temperature at core is 7227oC; 70% of fresh water is in glaciers, and many other facts. The

geosciences discoveries and their application (i.e. technology) helped to solve needs and

problems of human society. Earth System Science is the only science through which society

is directly connected, as stated below.

1. It sustains the society for its raw material requirements.

2. It gives better life to human race.

3. It helps us to understand global warming and environmental pollution.

4. It solves water crisis, faced by most nations.

5. It enables us to land-use planning in better ways.

6. It helps undertake waste-disposal problem in safer ways.

7. It educates us as to how inside and outside environment affects the Earth surface.

8. It develops our understanding about how Earth’s magnetic field protects us from solar wind.

9. It enables us to explore our space, ocean and land resources.

10. It gives us understanding of extreme weather (tornadoes, cyclone, hurricane, and

thunderstorm), and many related subjects.

Strange it may be, a large section of educated population in India is ignorant about the

basic idea of Earth Sciences and related activities which include Academic/Research (e.g.

understanding origin and distribution of resources), Developmental (making roads, bridges,

dams etc.) and Awareness (global warming, climate, water and environment). Since society is

facing scientific challenges in regard to natural resources including water, waste disposal,

environmental protection, natural hazards, land use etc., we must realize the role of earth system

science for social issues. Also, space research has taken a new trend while industries (oil and

mining) need interaction with geoscientists for their developments. Hence India must build

strong departments of Earth sciences with sustained leadership.

It is not enough that geoscientists carry out good research, exploring incredible history of

our planet by sophisticated technology and computer generated analogy. The educated public, in

particular the young scientific community, needs to have sufficient literacy in the Earth Science

in order to understand the discoveries, earth science scope and cross-discipline research

activities. To disseminate information about Earth sciences, we should celebrate Earth Science

Week by Photo Gallery, Posters, Model exhibition, Lectures, News Letters, Press releases and

Earth Science Teaching award. This would generate awareness amongst the school-going

students who do not have the subject of Earth System Sciences in the 10+2 curriculum; although

some knowledge about the rocks, fossils & environment is integrated into their General Science

courses in schools. However, Indian Institute of Technologies (IITs ) at Kharagpur, Mumbai,

Roorkee and more recently IIT- Bhubaneswar have full-fledged department of Earth sciences

where admissions are made on the basis of JEE results. Also, Earth science is a part of the 5 year

BS-MS dual degree programme in some of the recently established IISER (Indian Institute of

Science education and Research), particularly at Kolkata, Mohali , Bhopal, and

Thiruvanathapuram. Candidates after 10+2 can get admission if they have qualified Kishore

Vigyanik Protsahan Yojana (KVPY), JEE, and with high marks in State and Central Boards.

These institutes give integrated education of basic sciences including geosciences. The students

can thereafter seek post-graduation and PhD in some chosen branch of Earth sciences and

thereby can seek jobs in research institutes and universities in India and abroad.

It is interesting to know that Geosciences started as observational science using a

hammer, clinometer-compass and a microscope. Modern Earth Science education uses

sophisticated equipments and technological update. Newer courses of Remote sensing,

hydrology, environmental geology, engineering geology along with computer science offer

plenty of job opportunities. Co-operation with related fields, e.g. geosciences and civil

engineering offers job outside their fields. But the whole thing is centered on a committed and

competent faculty as also the modern equipments. The students should know that Geoscience is

the foundation for a rock solid career.

Chapter 1

The Planet Earth and its Cosmic Cousins

1.0 The Solar System

The solar system is the collection of planetary bodies that are gravitationally bound to the

Sun. The Sun is at the centre of the solar system and contains most of its mass—99%. At least 9

planets orbit the Sun. Moving outward from the Sun are Mercury, Venus, Earth and Mars, all of

which are rocky (terrestrial) planets. Next is the main Asteroid belt. Then there are the outer

planets in the order Jupiter, Saturn, Uranus, Neptune and the controversial Pluto. These are

gaseous planets composed mainly of hydrogen (H) and helium (He) gas. Almost all planets have

one or more moons which revolve around their planet. Beyond Neptune (and Pluto) lies the disk-

shaped Kuiper Belt of comets and assorted objects.

The planets orbit the Sun. They emit no light of their own, like the moon. They simply

reflect sunlight. The planets show a high order in their motion and positions. All planets travel in

elliptical orbits around the Sun, and except Pluto, all planets and their moon follow orbits that lie

roughly in the same plane. Furthermore, all the planets and almost all their moons orbit in the

same direction—counterclockwise when viewed from the Sun’s North Pole.

The Solar system, like the interior of an atom, is mostly empty space. We can only

comprehend the sizes and distances of the planets from the Sun if we reduce the size of

everything by a factor of billion. If the Earth is the size of a grape, its moon becomes pea-size

with a distance of about one foot or 30 cm from the Earth. The Sun becomes the size of a hippo

or rhino, having the distance of 150 m or one and a half football fields; Jupiter, on this scale has

the size of lemon with a distance of about 15 football fields away from the Sun. Pluto is about

the size of a mustard seed with a distance of 60 football fields from the Sun.

Because of these great distances, astronomers use the astronomical unit to measure them.

One astronomical unit (AU) is about 1.5x108 km---which is the distance from the Earth to the

Sun. Table 1 gives the distances from the Sun in km as well in AU and other details of the Solar

system.

Table1. Some general information about the planets of the Solar System.

Name Diameter Mass Av. Distance Time to Satellites

Km Earth =1 from Sun orbit Sun

(million km)

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Mercury 4878 0.05 58 88 days none

Venus 12102 0.95 108 225 days none

Earth 12756 1 150 365 days 1

Mars 6780 0.11 228 678 2

Jupiter 143,000 318 781 11.86 years 100+ ?

Saturn 121,000 96 1426 29.5 years 30+

Uranus 51,100 14 2879 83.7 years 21+

Neptune 49,500 17 4500 165 years 13+

Pluto 2390 0.002 5900 249 years 3

The above information about the solar system was obtained by the early observers of the

sky, and is the result of the observations by curiosity-driven human beings of different nations.

The stars observed in the night sky are grouped by Greeks, Babylonians and Indian astronomers

according to their country’s culture. The group of stars is called constellations. For example, the

group of seven stars that seem to rotate around the North Star is called ―Saptarishi‖ by Indian

sky viewers and sages, and Big Dipper by Greeks. Although the stars, as we know today, are at

different distances from the Earth but ancient astronomers conceived them as being attached to a

gigantic sphere surrounding the Earth. This is called Celestial Sphere---an imaginary sphere. It

is definitely a useful concept for visualizing motions of stars, which result due to daily rotation

of the Earth on its axis. The concept is also useful because it refers to the motions of celestial

objects as a whole and so it does not change the relative motions of these objects. The position of

North Star (Dhruva-tara, in Hindi language), around which Saptarishi or Big Dipper move,

remains stationary because it lies close to the projection of Earth’s rotation axis. This star

appears to turn around an imaginary N-S axis every 24 hours. Being at great distances from the

Earth, the stars appear as though they were all positioned on a celestial sphere. Astronomers

measure the vast distances between the Earth and stars by the measuring unit called Light years.

One light year is the distance that light travels in 1 year (or 946080000 seconds), about 10 trillion

kilometers.

[Speed of light is 3x108 meter/second; so in 365x24x60x60 = 946080000 seconds, the distance is

9460,000,000,000 km which on rounding gives 10,000,000,000,00 km = 1012

or 10 trillion km]

Light emitted by distant stars is seen after many days and if news is broadcasted from a

distant star of say 200 light years, we will have it on the Earth after 200 years—certainly not for

the present generation.

1.1 Early observers

Those persons who looked at the surface of the Earth were religious. They considered the

Earth as flat and centre of the Universe in which the Sun and other shining object revolve around

the Earth. This geocentric concept continued for several years. Because the Earth was declared

flat by these religious people, nobody could have believed at that time that we could reach

America by sailing eastward from Chennai.

Science could not have advanced under divine control

Some ancient thinkers who looked above at the sky had different view, because, as

Leonardo da Vinci said, ―all our knowledge has its origin in our perception‖. These observers

saw Earth’s shadow on the moon during lunar eclipse, saw the hull of the ship first and not the

sails or mast from distance, and many similar observations, all of which led them to conclude

that the Earth and other planetary bodies are oval and revolve around the Sun. The proponents of

this heliocentric or sun-centered theory were mainly a Pole, named Nicolaus Copernicus (1473-

1543) and a German scientist Johannes Kepler (1571-1630). Later, Galileo Galilei, an Italian

medical doctor turned Astronomer, supported this view by his crude telescope.

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That the Earth and other planets move around the Sun was one of the greatest human

achievements

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Subsequently, images from spacecraft have now conclusively proved that the Earth and

all planets and the Sun are not flat, and that all 9 planets revolve around the Sun.

In 5th

century, the Indian astronomer Aryabhatta also provided some useful physical data

for the Earth, its rotation, spin and orbits etc. Several physical data collected over time are:

Circumference = 39842.4 km

Diameter = 12766 (equatorial) and 12756 (polar)

Earth spin on its axis = every 24 hours with a speed of 1660 km/hr

Earth orbits the Sun in 365 days and 6 hours.

Earth travels 1,07,200 km per hour (around the Sun)

The volume of the Earth of the Earth can be calculated from radius (hint, 4/3 R3).

Initially there were 6 planets that were discovered by Astronomers, mainly by Galileo

with the help of telescope. But later a German astronomer based in England, William Herschel

found the planet Uranus by a detailed sky survey in 1781. Thereafter in 1846 the planet Neptune

was discovered and in 1930 Pluto was revealed.

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This was one of the most mind-changing discoveries in the history of Science as it showed that

the universe is dynamic place where new object might be found.

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Six of the 9 planets are orbited by one or more natural satellites called moon. The space

probes have brought detailed information on the satellites of the solar system (see Table 1).

1.2 Origin of planet Earth

The question of how the Earth originated is connected to the evolution of the Solar

system, which is 5 billion years old. Five billion years ago there was no Sun and no Earth and no

other planetary bodies of the Solar system. But the galaxy or the Universe is believed to have

existed 14 billion years ago. The region of the galaxy that would become our solar system was

dark, cold and almost empty. The pattern that is present in the Solar system suggests that the

origin of the Solar system is not accidental. Any theory of the Solar system formation must

explain the major regularities stated already and recalled here: (1) Orderly motions among the

planetary bodies of the Solar system and (2) The clear division of the planets into 2 main types

terrestrial (rocky) and gaseous.

A range of theories flourished in the 19th and 20 century. The most widely accepted

theory is the Nebular theory by Immanuel Kant and Pierre Laplace. According to this theory,

the Sun and planets formed together from an interstellar cloud of gas and dust, called nebula

(Latin for ―cloud‖). Initially the cloud or nebula was very diffuse and large, perhaps many times

the orbit of Pluto. Mutual gravitation between the gaseous particles resulted in an overall

contraction of this nebula. The immense gravity of this large cloud attracted more dust-and-gas

inward toward its centre. As the matter in the cloud fell in, it began to spin and became hot. Over

time the nebula (or cloud) collapsed (gravitational collapse) and began to condense. With the

collapse of nebula, it was heated up in accordance with the law of conservation of energy which

states that in the absence of external work input (or output), the energy (potential + kinetic)

remains unchanged. As a result, the gravitational potential energy of attracting particles

transformed to heat as the particles grew close together. The center of the nebula became dense

enough to trap the heat energy which no longer radiated away. The hot central core of the nebula

remained a protostar, later to become our Sun.

Objects in the space do not speed up or slow down unless the speed is changed by

something else. This is called conservation of angular momentum which is the product of

mass x velocity x rotational speed. Conservation of angular momentum is a crucial aspect of the

nebular theory. It is because of the conservation of angular momentum (inertia of rotation) that

the nebula spun faster and faster, like an ice skater pulling in her arms to increase spin. The cloud

maintained a constant mass as it shrank so that the gravitational force grew stronger and the

cloud (or nebula) took on a spherical shape. Under the influence of gravity, the shape of the

nebula changed from sphere to flattened disk, much like spinning a lump of dough on your hand

causes it to flatten. It is also possible that the nebula attained a net rotation due to rotation of

galaxy itself.

In the next step there was a passing star (from already existing galaxy) which sucked a

cigar-shaped mass of the nebula, which fragmented/separated into different sizes and later cooled

in space and yielded planets. The remaining hot, central mass of the nebula, the protosun, as a

clump of gases and dust became the Sun. The planets all orbit the Sun nearly the same way

because they formed from the same flat nebular disk. The direction in which the disk was

spinning became the direction of the Sun’s rotation and orbits of the planets. Thus we see that

nebular theory accounts for the formation of the planets and their clear divisions into two groups.

But current view is somewhat simpler and considers the origin of the Earth and the Solar

system in context of Big Bang theory advanced for the evolution of the universe.

1.3 Big Bang theory

The theory of Big Bang is about the origin and structure of the universe. It is our best

idea, telling us how the universe works and is due to George Gamow, although the name was

give by the British cosmologist, Sir Fred Hoyel in an attempt to ridicule it. Sir Hoyel along with

Herman Bondi and Thomas Gold believed in Steady State universe which is considered always

the same and is infinite and expected to remain infinite. Big Bang marks the beginning of both

space and time of our universe. The universe and all the matter in it are derived from a minute

singularity. It is considered as a point in which the mass-energy (ME) of the universe was

concentrated. With a gigantic explosion, called Big Bang, 14 billion years ago (14Ga), space

was created and the universe began to expand. The universe is considered as 4-Dimensional

analogue of the surface of an expanding balloon on the surface of which each point is moving

away from the other point, in an analogous way when we see ants on an expanding balloon

whereupon every ant sees every other ant moving farther away. This does not mean that each ant

is in a central position. In an expanding universe there is no inside or outside of the surface since

the surface is all that exists. The picture of expanding universe is based on the work of American

astronomer Edwin Hubble. It is assumed that the expansion only matters on cosmic scale and

does not affect the Solar system or even a whole galaxy.

Besides the expansion of the universe, the second line of evidence in support of the Big

Bang is the leftover heat from the Bag Bang—more formally known as the Cosmic Background

Radiation (CBR). CBR is a form of electromagnetic radiation. In 1965, the scientists Arno

Penzias and Robert Wilson at Bell Laboratory in New Jersey used a simple radio receiver to

survey the heaven for radio signals. They found that no matter which way they directed their

receiver, they detected microwaves with a wave length of 7.35 cm coming toward the Earth, with

no specific source of the radiation. Where were the microwaves coming from and why, was a

puzzle to Penzias and Wilson.

Theoretical physicists at Princeton University, working around the same time as Penzias

and Wilson, showed that if the universe began in a primordial expansion (as described by the Big

Bang) it would have cooled by now. This is because the initial universe which was smaller and

hotter by the filled-in hot fog of hydrogen plasma, grew cooler as the universe expanded,

resulting in the cooling of plasma and radiation. The atoms became stable and could no longer

absorb the thermal radiation and the universe became transparent. The photons (radiation) that

existed at that time and filled the larger universe became fainter and less energetic. This

radiation, as electromagnetic radiation, when observed by radio telescope, would appear

glowing. The glow would be almost the same in all directions, not restricted to any star or

galaxy or other object. Calculations by the Princeton physicists gave present temperature of the

universe to be 2.7 K (= -171.3oC). Any object at 2.7K would emit radiation. Thus, a universe of

this T would be expected to emit microwave radiation of just the frequency observed by Penzias

and Wilson. Thus, the microwave radiation observed by Penzias and Wilson was found to be

emitted by the cooling universe itself. This faint microwave radiation, now referred to as CBR, is

taken as strong evidence of the Big Bang. Both scientists, Arno Penzias and Robert Wilson, won

Nobel Prize for their discovery of CBR in 1965.

The CBR is anisotropic and hence looks different from different directions. This

anisotropy of the background radiation reflects the inhomogeneities and irregularities in the early

universe. These irregularities allowed atom to meet atoms and eventually to form entire galaxies

in the sky. These galaxies are not randomly distributed but form clusters and other patterns.

1.4 Galaxies

A galaxy is a large assemblage of stars, interstellar gas and dust and dark matter in the

core called black hole. The black hole forms the central mass around which the rest of the

galaxy rotates. Most astronomers believe those 10 to 15 billion years ago, galaxies formed from

huge clouds of primordial gas pulled together by gravity, similar to the formation of our solar

system. Galaxies are distinguished by their shape. For example spiral galaxy, elliptical galaxy,

disk-form galaxy. The galaxy we live in is a Milky Way Galaxy. It is a faint band of light that

stretches across the sky. When we look at this Milky Way, we are looking at the disc of our own

galaxy. It consists of closely packed stars, including the Sun. In the center of this galaxy is huge

black hole, the site where matter collapsed into a miniature version of the ―singularity‖ (from

which the universe itself sprang). The black hole forms the central mass around which the rest of

the galaxy rotates. The Sun takes about 225 million years to complete a single lap.

1.5 Formation of Earth and other planets

In the Milky Way Galaxy, the spinning gaseous disk surrounding the ―protosun‖ was the

source of material that would become the planets. As the disk was spinning, matter collected in

some regions more densely than in others. Because of their extra mass the atoms or particles of

gas and dust exerted a stronger gravitational force on one another than on neighbouring regions

of the disk. So they pulled even more material to them. When the atoms of the gas-dust stuck

together, shock waves were produced, accelerating atoms to velocities close to that of light.

These atoms through chemical reactions built up more complex molecules which gradually stuck

together to form lumps, called planetesimals. Planetesimals grew larger through countless

collisions until they became gravitationally stronger than surrounding matter, and finally the

planetesimals became full grown planets. The inner planets formed from materials that remained

solid at high temperatures. Hence the inner parts are rocky. The outer planets by contrast consist

mainly of hydrogen and helium gas that coalesced in the cold regions of the solar system, far

away from the Sun. In these cold regions of the solar system, the gravitational forces among gas

particles overtook the gas pressure that tended to disperse them. A German-led group of

scientists ran an experiment, called the Cosmic Dust Aggregation Experiment (CODG) on

NASA space shuttle to prove that dust particles in space can stick together in this way.

Observation on a very bright star, Pictor, with a good telescope shows that it lies at the centre of

a flat disc of muddy-looking dust. Similar dust discs have been observed around other stars and

they confirm that when a star forms it does not absorb everything around. Instead, some stars

form at the center of a spinning disc of material. Enough material is left over to produce planets

1.6 Characteristics of each planet

It is time that we know the characteristics of each planet of the Solar system. First we

give a brief account of the rocky or terrestrial planets followed by gas planets.

Mercury

It is closest to the Sun and hence is the fastest planet circling the Sun in only 88 Earth

days. It is slightly larger than the Moon. Mercury spins on its axis only three times for each 2

revolutions. This makes its day time very long and very hot with a temperature of 430oC.

Because Mercury is small and has a weak gravitational field, it holds very little atmosphere,

slightly more than a vacuum that most laboratories can produce on the Earth. Without a blanket

of atmosphere there is no wind to transfer heat from one region to another. Night-time, the planet

Mercury is very cold, ca.-170oC. It is seen as evening star during March and April and as

morning star during September and October. It is seen near the Sun at sunset and sunrise.

Venus

It is the second planet from the Sun. Venus closely resembles Earth. But it has a very

dense atmosphere and has an opaque cloud cover about 96% CO2. Thus it traps heat near the

Venutian surface. This plus the proximity to the Sun make the Venus the hottest planet in the

Solar system, with high T of 460oC and thus too hot for oceans. Venus takes 243 Earth days to

make a full spin, and only 225 Earth days to make one revolution around the Sun. This means

that a day on Venus lasts longer than a year on Earth. Venus spins clockwise, whereas the Earth

spins anticlockwise. It is the first star-like object to appear after the Sunset. So it is often called

the ―evening star‖. About 17 probes have landed on the surface of the Venus. From the

spacecraft data, we know that Venus has very active volcanoes and extremely harsh place.

Earth

The planet Earth is our home and is the blue planet, with more water than land. The Earth

orbits the Sun with its night side always facing away from the Sun. Our distance from the Sun is

just right to maintain an average temperature delicately balanced between that of freezing and

boiling water. Details are given in chapter 2.

Mars

This planet is slightly more than half the Earth’s size. It is similar to the Earth in having a

core, mantle, crust, and a thin cloudless atmosphere. It has polar ice caps and seasons that are

nearly twice as long as that on the Earth because Mars takes nearly 2 Earth years to orbit the Sun.

The Martian atmosphere is about 95% CO2 with only 0.15 % oxygen. It is thin to trap heat. So,

temperatures on Mars are generally colder than on the Earth, ranging from 30oC in day to -130

oC

at night. Some surface features on Mars, e.g. hollows, channels on Mars appear to have been

carved out of water. This is indicated from photographs sent to Earth stations by space ships or

spacecrafts fired by NASA ( Mariner 4, Viking, Curiosity Rover) and recently fired Mangalyan

by ISRO Indian Space Research Organization) on September 24, 2014. Mars have two moons—

Phobos and Deimos. Both have catered surface.

Outer planets are different from the inner rocky planets in having different size and

composition. The outer planets are gigantic, low-density planets. All have ring systems. Saturn

ring is most prominent. The rings were formed when comets or asteroids collided with a moon of

Saturn, shattering them into many pieces. These fragments spread out around Saturn and formed

the ring. We will consider the outer planets in the order of their distance from the Sun.

Jupiter

It is the largest of all the planets. Its atmosphere is 82% H, 17% He and 1% methane,

ammonia and other molecules. It is 11 times bigger than the Earth. Jupiter’s core is solid sphere

and 15 times massive as the center of the Earth. Jupiter has 28 moons of them Io has more

volcanic activity than any other body in the Solar system.

Saturn

It is10 times the Earth’ diameter. It has bright rings that are clearly visible with a small

telescope. The rings are composed of chunks of frozen water and rocks as remains of a moon

torn apart by tidal forces. Saturn has some 24 moons; largest is Titan.

Uranus

Its density is slightly more than that of water. The most unusual feature of Uranus is its

tilt. Its tilt axis is 98o to the normal of its orbital plane and hence it lies on its side. Uranus has 21

moons.

Neptune

It is 4 times the Earth in size. It has 8 moons in addition to the rings.

All these planets receive energy from the Sun. Earth receives about 1019

kilocalories sun energy

every day. Therefore, we should also know some salient features of the Sun.

1.7 Sun—the star of the Solar system

The Sun has 4.5 million tons of mass. The Sun’s core has 10% of Sun’s total volume. The

core is very hot, 1.5 crore degree Celsius. It is also very dense, 12 times the density of lead.

Because of enormous temperature, the gases H and He and minor quantities of other elements

exist in the plasma state. The energy from the core to the surface travels in the form of γ-rays and

X-rays. Overlying the core is the radiation zone in which these rays undergo countless

collisions with atoms. Above this zone is the convection zone which consists of low-density

gases that stirred by convection. The atoms of the gases are heated by radiation and form the

radiation zone. As the gases become hot and less dense, they rise to the surface in form of visible

light, UV, and infra-red radiations. The atoms of gases in the convection zone have lost some of

their energy as radiation, they therefore loose volume and become denser and hence sink back to

the radiation zone. There, the gases are heated again as they absorb radiation from the Sun’s

core. The heated gas atoms rise again, carrying energy from the bottom to the top of the

convection zone. They lose this energy at the surface by radiation and sink again. The visible

region of the Sun is its surface which is a glowing plasma region of ca. 100 km thick. It emits

most of the light we see is known as photosphere. Here, there are also relatively cool regions

that appear as spots when viewed from the Earth. These are Sunspots. They are cooler and darker

than the rest of the photosphere. They are caused by magnetic fields. The form of solar magnetic

field is not constant. A reversal of magnetic poles occurs every 11 years when the number of

sunspots also reaches a maximum number. Sunspots can be seen by unaided eye when the Sun is

low enough on the horizon. Sunspots are typically twice the size of the Earth. They move around

due to Sun’s rotation and they last about a week or so. Above the photosphere is a 10,000 km

thick layer of plasma seen as a pinkish glow around the eclipsed Sun. This layer is called

chronosphere. Beyond this is a region of Sun’s corona---a shell of plasma of several million

kilometers. This shell merges with what is known as the Solar wind---a whirl of high-speed

protons and electrons. It is the solar wind that produces the tails of the comets and aurora

borealis on the Earth.

In a similar way the Sun originated, all stars are also born from contracting nebula but

they do not progress through the lives in the same way. Stars become dense by mutual

gravitation between the gaseous particles. Being dense, the center of the nebula traps radiation so

this energy is not radiated away. The hot central core of the nebula becomes a protostar. All stars

have much in common with the Sun. Since all stars are born from interstellar dust, they have the

same composition as the Sun, i.e. each star has about 75% hydrogen and 25% helium plus some

heavier elements. Stars shine brilliantly for millions or billions of years because of nuclear fusion

reactions that occur in their cores. When nuclear fuel exhaust, the stars die. Stars differ in their

brightness and colour. Brightness relates to how much energy a star is producing, while colour

indicates its surface temperature. Blue star is hotter than yellow star which is hotter than red star.

Stars brightness is also dependent on how far it is from the Earth.

1.7.1 Chemical composition of the Solar System

The galaxies and their stars and other planetary bodies are formed of different elements.

Measurement of different elements in the universe provides one more evidence for the Big Bang.

The universe is found contain about 74% of hydrogen (H) and 26% of helium (He) by mass.

These two elements are the lightest elements. Hydrogen is the simplest possible atom, consisting

of a proton (a positively charged particle) orbited by negatively charged electron. Helium atom is

the next simplest atom whose nucleus contains 2 proton and 2 neutrons (neutral with no charge).

The amount of helium in the universe is in agreement with the theory and is the principal

evidence that the Big Bang happened. This was revealed from the analysis of the spectra of stars

by Cecilia Payne in 1925.

But looking at the Earth we find that it is principally made up of Oxygen (O), Silicon

(Si), iron (Fe), magnesium (Mg) and few other elements namely calcium (Ca), potassium (K)

and sodium (Na). Over 47% of the Earth crust (top most layer) is oxygen and 28% by weight is

silicon. There is quite a bit of hydrogen in the water (H2O). But helium is so rare, and is now

extracted from natural gas. Lithium (Li) is found in parts per million (ppm) amounts. Lithium

has some high-tech uses such as the ability of Li(OH) to absorb carbon dioxide (CO2) and

prevent astronauts from asphyxiation. Lithium is hardly important for life although we use it in

battery cells.

1.8 How were all the elements of periodic table formed?

The answer is that nucleosynthesis occurred in the universe. The theory of nucleosynthesis is one

of the great achievements of 20th

century. The term simply means the synthesis (or fusion) of

nucleus—the central core of atoms. Nuclear fusion can be understood as a kind of nuclear

reaction in which lighter atomic nuclei combine to form heavier nuclei. All fusion reactions

release energy because the total mass of reactants is greater than the total mass of the products.

The mass lost in the reaction is converted to energy in accordance with Einstein’s famous

equation, the mass-energy equivalence, E = mc2. Fusion brought about by high temperatures is

called thermonuclear fusion and takes place in our Sun by fusing 4 hydrogen nuclei to form one

helium nucleus. The resulting helium has 99.3% of the original hydrogen mass. The difference in

mass is converted to energy which radiates away from the core in form of gamma and X-rays. At

the surface, much of this energy is emitted as light, a tiny bit of which reaches our planet Earth.

The basic assumption here is that once the nuclei are there, the electron required to orbit them

will come as a result of electromagnetic force.

Nucleosynthesis occurs when a star, like the Sun, attains very T, about 10 million Kelvin

(106K). At such high temperatures the hydrogen is ionized or stripped of their electron and

protons, thus creating plasma of free electrons and protons. Plasma is a state of matter similar to

gas except that it consists of ions and electrons rather than atoms because high energies have

stripped of their electrons. In this process, hydrogen nuclei begin to form helium nuclei when 4

hydrogen nuclei (or protons, P) fuse to form one helium nucleus (2P+2N). The process is called

―hydrogen burning‖ a kind of nuclear fusion, and is the same force that powers a hydrogen

bomb. A star’s hydrogen burning lasts for a period of a few million years to 50 billion years,

depending on its mass. A star with a mass less than 0.08 times the mass of the Sun would never

reach the temperature of 10 million Kelvin, the threshold needed to sustain fusion of hydrogen.

The process of nucleosynthesis, taking place in stars at early stage of Big Bang is called Big

Bang Nucleosynthesis. It is shown in the following steps for simplicity.

P + P = PN + e + v (1)

H H Deuterium positron neutrino

PN + P = PPN + energy (2)

Helium 3

PPN + P = PPNN + energy (3)

Helium 4

This thermonuclear reaction converting H to He, releases an enormous amount of

radiation and thermal energy (for reaction H burning gives 1.442 MeV, according to Hans Bethe,

1939). Outward-moving radiant energy and the gas accompanying it exert on an outward

pressure, called thermal pressure on the contracting matter. When nuclear fusion occurs fast

enough, thermal pressure becomes strong enough to halt the gravitational contraction. At some

point, outward thermal pressure balances inward gravitation pressure, and the star’s size and

mass stabilize. In this situation, the collision of 2-Helium to form a stable nucleus of a newer

element is not possible, because it needs higher temperature since He nucleus has twice electric

charge of H. Stars, like the Sun, never achieve hot enough cores to permit these transmutations

to go very far. But for stars with masses above 10 times that of the Sun’s mass gravity

overwhelm thermal pressure and the star pulls inward. As the burn out H-core contracts due to

gravity, the T rises. At a certain point, the T becomes high enough in the core to begin He-

burning—the fusion of 3He produces C atom which, in turn, form Oxygen (when these C nuclei

accumulated other particles). The star then has a structure of concentric shells. Helium fuses to C

at the Star’s centre while H fuses to He in the surrounding shell. As fusion continues, C will

continue to accumulate in the star’s core, but T will never become hot enough to allow C to

undergo fusion. Now gravity takes over and the star contracts which boosts its temperature. The

star continues to emit vast amounts of energy. With further combinations of more neutrons and

protons as stars burns, the end result is getting atoms heavier, until we have iron (Fe) and Nickel

(Ni)—two of the more abundant metals---marking the final process of Stellar Nucleosynthesis.

It is for this reason that we have abundance of Fe and Ni in meteorites and Earth’s core. The star

now has an onion structure by the chains of transmutation. The iron (Fe) nucleus (having 26

protons) is more tightly bound than any other element. This happens in older and hotter stars

than the Sun, which we call Red Giants or Red Supergiants. The star can shrink no more

because electron cannot be pushed more than a threshold value. The star stabilizes and will no

longer be producing energy. The star therefore faces energy crisis. The consequences are

dramatic. When the core density becomes so great that all the nuclei are compressed against one

another, the core implodes. Such a stellar explosion is a supernova---a most spectacular event in

Nature. This violent explosion hurls into space the elements previously manufactured over

billions of years. The supernova elements are captured by the existing nuclei in the stellar cloud.

The whole collapse is catastrophic and lasts only for a few minute. It is during this brief time that

the heavy elements beyond iron are synthesized to produce such elements as silver (Ag), gold

(Au), and uranium (U). Remember that these elements for which we have a craze originated

from ashes of the ancient stars. The super-stellar origin explains why elements that are precious

to us are very rare in the universe overall. The inner part of a supernova star becomes a neutron

star which provides an explanation for the existence of Pulsars which are source of low-

frequency radio emissions.

When nuclear fuel of a star exhausts, the star dies. These dead stars are called white dwarf and

are produced form low to medium size stars which have burnt out their nuclear fuel. The white

dwarf cools for millions of year in space until it becomes cold and radiate visible light.

1.9 Asteroid Belt

During planet formation of the Solar system, some cosmic material is never swept into

the planet formation. The reason for this that the light or photons emitted from the Sun stops

more dust and gas to fall in. This scrap material forms the asteroid belt which contains objects

like comets, asteroid, meteorites which are observed in the sky. Nebular theory predicted about

the location of this asteroid belt between Mars and Jupiter.

1.9.1 Asteroids are small, rocky bodies that orbit the Sun. Asteroids are in a way minute planets.

The asteroids are in large number and are of different sizes, but none is larger than the size of the

Moon. The biggest asteroid called Lutetia is heavily cratered when photographed by Rosetta

Mission of the European Space Agency.

1.9.2 Comets, like asteroids, orbit the Sun. They differ from asteroids in chemical composition.

Comets are not rocky but dirty snowballs which consist of water, methane or ice in which chunks

of rocks, metals and dust are embedded. There are two groups of comets in the Solar system.

One is the asteroid belt and the other is the Kuiper Belt orbiting the Sun in a track beyond the

orbit of Pluto. As the comet approaches the Sun, solar heat vaporizes its ice which glows and

seen as a luminous tail called coma.

1.9.3 Meteorites: our cosmic visitors

A piece of debris chipped off from an asteroid or comet is called meteoroid while a

meteor is meteoroid that strikes the Earth’s atmosphere about 80 km from the Earth’s surface. It

is seen as a falling star or a flash of light. When it reaches the ground it is called meteorite.

Meteorites that have been found on the Earth are either Stony or Iron-based. Some of the Stony

meteorites look unaltered material from the early solar system. But others look more like

terrestrial rocks. To explain their presence this way, it is conceived that they were built into a

planet that later fragmented. Similarly, the iron meteorites contain patterns that show that they

must have cooled slowly, probably in the core of an Earth-like planet which fragmented to

release this stuff of iron meteorite. There are even a few ―stony-iron meteorites that seem to have

come from the boundary between the iron core and the rocky outer layer of a planet. This planet

must have long gone from the early solar system. This must have been much smaller than our

planet Earth, and it also never had oceans and life, unlike the Earth.

On the ground the stony meteorites appear darker than most Earth’s rocks. And iron

meteorites may look shiny and will be unusually heavy for its size. Meteorites never occur alone.

They tend to occur in several pieces, scattered in fields. So if you find one, you should find more.

The most distinctive meteorites are the chondrites which show spotty bits---called chondrules.

If one finds a freshly fallen meteorite, one should put it in a plastic air-tight bag so that its gases

are not lost and scientists can analyze the ―original‖ or unchanged cosmic material—the

meteorite. Meteorite as space probe carries with it history of events in the universe over the 5

million years.

1.9.4 Meteorite impact

When meteorites fall on the ground their evidence is seen in a crater—better called

impact crater. About 170 impact craters are recognizable on the Earth such as Arizona crater in

USA, Yucatan peninsula of Mexico, Lonar Crater Lake in Maharashtra, India, and many others.

On February 14, 2013 a meteorite fell in Siberia (Ural Mt.), injuring about 1000 people.

There are various ways to distinguish the impact crater from that resulted from an eroded

volcanic vent, or a sink hole formed by dissolution by rain or erosion by sea.

In impact craters one can see a succession of ring-shaped ridges in which the rock

materials have been bodily uplifted by the impact, like a car bonnet in a head-on collision. Other

evidence is deep layer of breccias or shattered rock within the crater itself. Sometimes one finds

tektites which are glassy masses formed by the impact and then flung away as scattered stuff

near the margin. In some shattered rock pieces we find a characteristic silica mineral called

stishovite (SiO2) which has very high P stability.

Some geologists considered the meteorite impact as a cause of extinction of dinosaurs

and millions of other species about 65 million years ago. This was supported by the findings of

traces of the metal iridium at the top of the rock-sequence of Cretaceous age (about 65 million

years old). Iridium is rare on the Earth but s associated with meteorites. The Swiss geologist

Walter Alvarez started to find iridium in various sites around the Earth in Cretaceous rocks, just

the places where the dinosaurs vanish. This all sounds very satisfying. But how does a meteorite

impact in Central America (Arizona) kill off the dinosaurs in Europe? Surely, meteorites are the

cause of devastation as in 1908, a rocky meteorite when struck Tunguska area in Siberia

devastated an area of several hundred kilometers, was heard several kilometers far and divested a

large area. Such an impact must have killed millions in the past in smaller area but not globally

vast areas.

Some other theories were advanced for the mass extinction of the dinosaurs and we shall

discuss in chapter 2. But as the nuclear explosion hurls vast amounts of dust into atmosphere

directly and ignites fires, not allowing sunlight to reach the Earth’s surface, meteoritic fall might

alter the climate fatally, causing extinction of dinosaurs.

1.10 Moon

This is one satellite that orbits the Earth. It spins once every 27 days about its own polar

axis as often as it revolves around the Earth. This is the reason we see the same side of the Moon

encircling the Earth. About 16% of the Moon’s surface is covered by big round areas, called

Maria (mare in Latin is sea) by early astronomers, although no ship ever sailed on them. The

Maria is solid layers of lava produced at the late stage of the Solar system when the Moon was

bombarded by large planetesimals. Their impact produced such heat that the immense craters

they generated filled in with molten rock. Today they are smooth because they were solidified

that way. By contrast, the rest of the Moon is made up of highlands which have survived from

the earliest days of the solid Moon. They have been cratered and at many places new craters have

obliterated older craters beneath them.

On the origin of the Moon, many scientists believe that a Mars-sized rock body (as

unaccreted rock debris orbiting the Sun in the early history of the Earth) collided with the Earth,

about 20 million years after the Earth had formed. Material blasted out from the Earth, which

formed the Moon. This idea is known as the Giant impact Theory of the origin of the Earth’s

Moon. The Moon is too small to have an atmosphere and is therefore without weather. Also, the

Moon being too small, it has little gravitational pull to have an atmosphere and is therefore

without weather. The only eroding agent has been meteoritic impacts. More information about

the Earth’s moon will soon be obtained from Chnadrayan-2 launched by Indian Space Research

Organization (ISRO) on 22nd

July 2019.

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Chapter 2

Geosphere, our Deep Earth

2.0 The Earth beneath our feet

In chapter 1, we have understood the origin of the planet Earth which formed about 4.6

billion years ago from debris orbiting the Sun. In this process some of the debris (dust and cloud)

collided and fused into a rocky mass forming rudimentary Earth. Each time material from space

collided with Earth and attached to it. The kinetic energy of the impacting bodies transformed to

heat. Consequently, Earth became molten and thus had the ability to flow due to convection

currents that continued to prevail in the molten Earth. Under the influence of gravity, dense and

heavy iron-rich matter sank to the Earth’s center to become the core. Less dense, silicon- and

oxygen-rich material rose toward the surface by differentiation—the process by which gravity

separates materials of different densities. This differentiation during fluid state of the Earth gave

rise to different layers--crust, mantle and core. Finally, the frequency of the impact (of debris)

slowed and the Earth cooled. Remember that when the planet was molten there were no rocks.

Later when the Earth’s surface cooled, there was crystallization of minerals which on

consolidation formed rocks. The first rocks to appear were igneous rocks—those formed

directly from the crystallization of magma (molten rock) or lava. Finally, we got a solid ball of

the planet Earth with a circumference of nearly 40,000 km and diameter of 12732 km. This gives

509 million square kilometer surface area of the Earth, including its land, ocean and ice.

2.1 Earthquake revealed Earth’s interior

A few thousands of kilometers below our feet, a lot of things are happening even today,

which influence our everyday life. The information underneath the Earth’s surface is obtained by

earthquake. Earthquakes are caused by stress (or force) applied to rocks at some place in the

Earth’s interior. The stress results into strain (compression or tension) and the rock undergoes

deformation such that it reaches its yield point—the breaking strength. At this point the rock

suddenly breaks loose and slips into a new position. As a result, the stored elastic energy is

released in form of seismic waves which travel through the rock. The study and measurement of

seismic waves or the science of earthquake is called Seismology. The actual site of initial

slipping of rock is called the focus of an earthquake. The seismic waves radiate out in all

directions from the focus, like sound from a ringing bell. The point at the Earth’s surface directly

above the focus is called the epicenter.

Seismic waves, like any other kind of wave, reflect from surfaces and refract through

other surfaces. This reflection and refraction together with variations in speed and wavelengths

(symbolized, λ, lambda) reveals much about the medium in which these waves travel.

Seismic waves are two main kinds. (1) Body waves which travel through the Earth’s

interior, and (2) Surface waves which travel on the Earth’s surface like ripples on water. Body

waves are further classified into two varieties: (a) Primary waves (P-waves) and Secondary

waves (S-waves).

P-waves are longitudinal waves. They compress and expand the material through which

they travel. These waves are the fastest seismic waves, travelling at varying speeds (between 2

and 8 km per second), depending on the nature of Earth’s material—fluid, magma or solid rock.

S-waves, on the other hand, are transverse waves. They vibrate the particles of their

medium up and down and side-to-side. They travel more slowly than P-waves. S-waves can

travel only in solid materials; they cannot travel in liquid medium.

Surface waves travelling on the Earth’s surface are of two types. (i) Rayleigh waves and

(ii) Love waves, each named after its discoverer. Rayleigh waves roll over and over in a

backward tumbling motion, similar to the ocean waves, except that ocean waves tumble in a

forward direction. Love waves travel just like S-waves, except that the shaking is horizontally

side-to-side. As a result of this side-to-side shaking, Love waves are damaging particularly the

tall buildings.

There are several ways to assess the strength of an earthquake, for example from the

quantity of damage by earthquakes at a specific location. But the size of earthquakes in terms of

their magnitude is a better method, first suggested by Charles Richter. This magnitude scale is

called the Richter scale, after its proposer. Richter’s magnitude is a measurement of how much

the ground shakes during an earthquake. Richter scale is logarithmic to accommodate the wide

variation. A magnitude 7.0 earthquake shakes the Earth 10 times more severe than a magnitude

6.0 earthquake but 100 times more severe than a magnitude 5.0 earthquake. The instrument that

measures this magnitude is called seismometer. In India we have placed a number of

seismometers at different locations to measure earthquakes. One must note that we cannot

predict earthquake. Scientists can only measure the build-up stress in rocks and so predict a

likelihood of an earthquake.

Earthquakes occur all over the world and are as devastating as they are common. Most

earthquakes occur along circum-pacific region—called the Ring of Fire—the site of abundant

volcanic activities all over this region since crustal (lithospheric) plates occurring in this region

have movements in different directions.

A powerful earthquake occurred on December 26, 2004. The earthquake originated

beneath the Indian ocean, off the western coast of Sumatra. This location marks the boundary

between subducting or down-going Indian plate and the overriding Burma plate. Although the

earthquake itself caused severe damage and casualties, the aftermath of it was even more

devastating. With its epicenter beneath the Indian Ocean, the earthquake generated huge seismic

sea waves—the tsunami. The coastal areas throughout the Indian Ocean basins were damaged.

This tsunami killed about 200,000 people in Indonesia and other adjoining countries.

2.1.1 The Earth’s interior was probed

By the end of 19th

century a massive earthquake occurred in India (Assam earthquake of

12th

June 1897). An Irish geologist, Richard D. Oldham, working in India was examining the

records of this massive earthquake. He observed that its S-waves travelled some distance through

the Earth and then stopped. He also observed that the P-waves travelled as far as the S-waves

into the Earth but then refracted at an angle and lost speed. With the knowledge that S-waves

cannot travel through the liquid but P-waves can but at a reduced speed, Oldham inferred that;

the earthquake waves had hit an internal boundary---a place where the solid Earth becomes

liquid. He had discovered that the Earth has a distinct core.

Following this discovery, a Pole seismologist Andrija Mohorovicic (pronounced

mohorovuchick) analyzed seismic records from an earthquake near his home town of Zagreb (in

Croatia). He detected a sharp increase in the speed of seismic waves at another boundary that lay

at shallower depth within the Earth. He disclosed that the wave speed increased because the

wave was passing from a low-density solid to a high-density solid. Mohorovicic discovered in

1903 that the Earth is composed of a thin, outer crust that sits upon a layer of denser material, the

mantle. This dividing line between the Earth’s crust and mantle is called the Moho

Discontinuity or ―Moho‖ ever since.

In 1913 a seismologist named Beno Gutenberg substantiated Oldham’s findings by

showing that the mantle-core is very distinct and is located at a depth of 2900 km. He found that

when P-waves reach this boundary they are refracted so strongly that the boundary casts a P-

wave shadow over part of the Earth. This shadow is a region where no waves are detected. The

core-mantle boundary also casts an S-wave shadow that is even extensive than the P-wave

shadow. This indicated that S-waves are unable to pass through the core. And since S-waves are

transverse and unable to pass the liquids, Gutenberg realized that the core, or a part of it, must be

liquid.

Taken together the discoveries of Oldham, Mohorovicic and Gutenberg show that the

Earth consists of 3 layers of materials, each of different composition. These layers are crust,

mantle and core which collectively constitute what we call Geosphere. Each layer is a

concentric sphere so that overall the Earth’s structure resembles that of a boiled egg.

This simple picture of the Earth’s layers was refined in 1936 by Madam Inge Lehmen, a

Danish seismologist. Her research showed that P-waves refract not only at the core-mantle

boundary but again at a certain depth within the core, where they gain speed. The way in which

P-waves refract within the Earth’s core suggested that the core actually has two parts—a liquid

core and a solid inner core.

2.2 Earth’s layers

Seismology thus revealed the layered structure of the Earth. Each of the Earth’s layers is

described in brief for their characteristics.

2.2.1 Crust

The crust is the Earth’s topmost layer. It is thin, brittle and can crack. The crust has two

distinct regions: oceanic crust and continental crust. These are made up of different rock types.

The oceanic crust is dark, dense and formed of fine-grained rock named basalt. The oceanic crust

is about 12 km thick.

The continental crust, on the other hand, is composed of mainly granitic rocks that are

light coloured. The continental crust is generally 35 km thick.

2.2.2 Mantle

It constitutes about 87 % of Earth’s volume and 65% Earth’s mass. Like the crust, the

mantle is rocky, made up of high density rocks called peridotite, constituted of mainly pyroxene

and spinel and/or garnet. These mantle rocks, therefore, contain heavier elements such as Fe, Mg

and Ca. Hence the mantle is denser than the crust. The mantle also gains density due to the

weight of the overlying crust which compresses it. Weight increases pressure and minerals are

squeezed to have denser structure.

Although the mantle has a fairly uniform composition, it is divided into two different

regions, based on their physical properties. The upper mantle extends from the crust –mantle

boundary (i.e. Moho) to the depth of 660 km depth. The lower mantle extends from 660 km to

the depth of 2900 km at the mantle-core boundary.

Greater details from seismic studies showed that the upper mantle, at a depth of 150 -200

km is viscous, above which the crust and its underlying mantle of ca. 150 km depth act as a

single layer of relatively rigid rock. This 150 - 200 km thick part of combined crust and upper

mantle above the viscous layer (named Low Velocity Zone or LVZ) is called the lithosphere.

Beneath the lithosphere the viscous layer is called asthenosphere which flows in a plastic

manner, similar to silly putty which acts like a solid under sudden stress but behaves like a fluid

when stress is applied slowly. The rigid lithosphere behaves like a raft on the slowly flowing

asthenosphere and is thus responsible for the movement of lithospheric plates.

2.2.3 Core

The core is at the centre of the Earth and has a radius of about 3500 km. The core is of

the size of the Moon and occupies up to 15% of the Earth’s volume and 30% of its mass. The

core is twice as dense as the mantle because it is made up of metallic iron. Iron is much heavier

than O2 and Si in the crust and mantle. The core consists of two layers—the solid inner core and

liquid inner core. The inner core is solid because of very high pressure, about 14 million times

the atmospheric pressure at sea level and hence it is densely packed. It has temperatures in the

range of 3900oC to 7200

oC, thus as hot as the Sun’s surface. There are two main sources of heat

in the Earth’s core. (1) Heat generate during the ―Great Bombardment time‖ in the early history

of the Earth when chunk of space debris crushed into the Earth and the energy of these impacts

was largely converted to heat. (2) The transformation of gravitational potential energy to heat as

dense material, mainly iron sank to the centre of the planet Earth in its differentiation history. A

minor contribution could also be due to decay of radioactive elements which produce energy that

converted to heat. To some people it may be a curios question as to why the inner core is solid if

it is so hot. The answer is that immense pressure from the weight of the overlying earth layers

prevents inner core melting, analogous to the case of pressure cooker where high pressure

prevents high temperature water from boiling. The high pressure results into packing of atoms

too tight there to flow as a liquid.

2.3 Earth’s magnetism

The outer core has mainly iron and nickel and some sulfur and oxygen etc. and resembles

metallic chondrite. The outer core has less weight on it. Consequently the iron and nickel that is

above the inner core are molten. This molten layer is 2200 km thick. The movement of this

molten metal is responsible for generating the Earth’s magnetic field. As the Earth rotates, the

liquid outer core spins. Convection current starts in the outer core. The moving iron and other

metals in the outer core produce a flowing charge or current which creates Earth’s magnetic

field. As long as there is energy in the core to keep the iron moving, there would always be a

magnetic field. As a result the acts like a huge permanent magnet.

Perhaps the most unexpected finding of several decades of seismic studies is that the

inner core does not share the same 24 hours rotation as the rest of the Earth, including you and

me. Instead it is rotating slightly faster by 20 km a year. The rotation became apparent because

the whole of the inner core has a structure in which the iron crystals point N-S and earthquake

waves move through them faster in this direction than E-W direction. These aligned crystals

form a ―fast track‖ for seismic waves. Remember that the movement of liquid and solid metals in

the outer core helps to create Earth’s magnetic field. The roughly N-S alignment of the field

drags any small magnetized object into line with it. The Earth’s magnetic field is governed by

three components: (1) movement of the liquid, (2) an electric current, and (3) a magnetic field. If

two are there, the third will come into being. It works on the principle of dynamo used to

generate electricity. When a metal wire is moved in a magnetic field, a current is created. The

same principle is behind a power station. So if a magnetic field is applied to a wire with

electricity in it, the wire responses in its movement.

In case of the Earth, there is a convective movement of metal. And all these moving iron

have an electric current. Hence, there results a magnetic field. The Earth’s magnetic field is not

very powerful. It is rated at 0.0005 tesla (unit of magnetic field). Remember that magnetic

imaging machines in hospital have magnetic field more than 1.5 tesla (abbreviated 1.5T).

It is hypothesized that the Earth’s magnetic field is produced by a bar magnet in the

centre of the Earth, slightly displaced from the axis of rotation. This hypothetical bar magnet is

oriented with its south pole directed toward the north Magnetic Pole. As a result, north of the

compass needle points to the Magnetic South that makes a slight angle with the geographic

north. Scientific records of hundreds of years show that the relative position of the Earth’s

rotation axis and the magnetic axis has changed a few degrees. Remember that the intensity and

direction of the Earth’s magnetic field vary from place to place on the surface of the planet Earth.

Earth’s magnetic field is not fixed although there is the inertia of billion of tones of molten iron.

The field changes direction over a few thousand years. Inferences from solidified lavas indicate

that average time between reversals is 25,000 years. The last reversal was 78000 years ago.

We do not fully know how this reversal occurs. But it has something to do between

turbulent eddies in the outer core and the base of the Earth’s mantle. This can produce patches

of trapped molten iron in which magnetization is opposite to the main strength of the magnetic

field. Such a patch of ―reverse polarity‖ might eventually spread to occupy the region of one

magnetic pole while the second reversed its polarity. It is also possible that impact of heavy

meteorite or asteroid could cause magnetic reversals as the impact sends shockwave into the

core-mantle boundary.

The Earth’s magnetic field is not so powerful but its effects are deep into space, about

one lac kilometer (100,000km) above us. This magnetic field interacts with the Sun’s radiation.

And the results of this interaction are very interesting.

2.4 Sun emits Electromagnetic Radiation

The Sun bombards the Earth with more than light. This was disclosed by the discovery of

infrared light by William Herschel (who discovered the Uranus). He used a prism to separate out

sunlight into the spectrum, VIBGYOR (violet, indigo, blue, green, yellow, orange, red), similar

to that used by Isaac Newton about century ago to demonstrate that white light (sunlight) has 7

components. But Herschel placed a thermometer beyond the red end of the spectrum and found

that the temperature rose. He had indeed discovered infrared light---below the red end of the

spectrum. This discovery was one of the corner stone of the science of astronomy. As our

knowledge advanced we found that the Sun emits a wide range of energy in from of particles

(photons, positrons, electrons or β-articles, and α-particles or protons) and waves of different

wave lengths from gamma (g) rays, X-rays, ultra-violet (UV) rays, visible light, infrared,

microwave and radio waves, in the order of increasing wave length (10-6

nm to 103

m) and

decreasing frequency (10 22

to 102 herz). The g-, X- and UV- rays radiations from the Sun are

low in power but they have important effects. The most important is that they react with the

upper atmosphere and produce a layer of charged particles called ionosphere. This layer has the

property of reflecting radio waves. Unknown in late 1930s, the British Army Group mistakenly

considered the jamming of their radar by the Germans during the World War II while it was

being done by the particles emitted from the Sun.

2.4.1 Solar wind

The particles from the Sun flow constantly and are named as Solar wind whose

composition is thus similar to that of the Sun. That is, the solar wind contains large numbers of

protons and alpha particles (nucleus of hydrogen and helium) as well as electrons. All these

particles carry electric charges. They emit maximum energy during Sun-spot activity (which is

magnetic in origin) which results into mass ejections of these particles (in plasma state) from the

Sun. These particles as solar wind stay away at a safe distance of approximately 1 lac km from

the Earth’s surface, because Earth’s magnetic field diverts them from the surface of the Earth.

This is how mother Earth protects us from being destroyed by high energy particles.

When these charged particles, travelling toward the Earth, are diverted they arrive at a

feature called the Bow Shock where the Earth’s magnetism diverts them around the Earth. Since

these particles arrive in several million tones quantity, they exert pressure and the Earth’s

magnetic field is hindered from spreading into space. But a balance occurs between the incoming

solar wind and the Earth’s magnetic field. The place where these two are matched in strength is

called the magnetosphere. It is an oval field around the Earth. At this balanced place, a hot layer

of charged particles is formed, called magnetosheath.

Since the magnetosphere (the bubble of magnetism that surrounds the Earth) is not

spherical, some particles, however, find their way towards the Earth’s surface. Since the Earth’s

magnetic field is roughly aligned with the Earth’s rotation axis, the lines of force emerge out of

the Earth’s surface in Arctic and Antarctic and make loops in space to join up. The charged

particles then run along these loops and in so doing they come close to the Earth’s surface at

regions called the Polar cusps. Here, these particles are fed into the ionosphere existing in the

upper atmosphere. Space scientist van Allen from USA, while experimenting with satellites in

1958, found that these particles spread into two layers, called inner and outer van Allen belts.

Because the Earth’s magnetic field is not symmetrical, there is a spot in space about the South

Atlantic where van Allen Belts get closer to the Earth’s surface. This situation is dangerous for

space travelers, and hazardous to electronic equipments.

The charged particles penetrating the Earth’s magnetosphere, ending up in the Van Allen

Belts, overflow and move toward the N and S magnetic poles, along the lines of force of the

Earth’s magnetic field. As they get lower, they meet the upper atmosphere and interact with the

electron in the air molecules far above our heads. The result is amazing lights called aurora--the

Aurora Borealis in the northern hemisphere and the Aurora Australis in the southern hemisphere.

Any time we see an Aurora, it is more than 100 km above our head. It is characteristically green

but also red, created by charged oxygen atoms. Blue color is also seen from charge nitrogen

atoms. These colours correspond to the amount of energy emitted when an electron around

oxygen or nitrogen atom absorbs energy from the solar particles and then falls back again to its

orbit. The shapes of aurora can be arc, bands and coronas which can change rapidly and bewilder

the humans.

2.5 Reading Earth’s past in rocks

Scientists found ancient lavas having glassy crust to suggest that molten lavas were

chilled rapidly underwater implying that there was water on the earth from early times. A

corroded zircon of 4.4 billion years age in metaconglomerate from Neyerrer Complex in Western

Australia also suggests that water was present since the time the upper surface of the Earth

became solid. Radioactive studies and lava flows offer evidence that there has been abundant

water throughout Earth’s history. This water may have come from remote, i.e. from comets and

asteroids that collided with the Earth in its early period. Some scientists argue that the ocean

water came from the Earth itself, from the Earth’s mantle. This proposition is considered more

probable because, after the formation of the planet Earth there was an intense period of volcanic

activity. This released large quantities of water vapour (and other gases) into the atmosphere. As

the Earth cooled below 100oC, the water vapour in the atmosphere condensed to form clouds and

eventually formed rain, filling the hollows and large low-lying regions –the oceans

The rain water in particular broke down the already formed igneous rocks by the physical

and chemical processes, causing weathering and erosion of the igneous rocks. The material

released by the action of rain produced different sizes of sediments which were transported and

deposited on the ground and sank to the bottom of sea water. Here, deposition occurred with

largest grain at the bottom and smaller grains at the top (geologists call it graded bedding). These

sediments were laid in horizontal layers which is called bedding in geological terminology.

Sediments are classified by their mode of formation, for example, sandstone (clastic material),

chalk and limestones (biochemical), and salt and other evaporates (chemical). Once living plants

and animals when died were also entombed in these sediment layers which are now seen as

remains or fossils preserved in the sedimentary rocks. The exposure of sedimentary rocks from

ocean depths is caused by natural upheavals or diastrophic movements followed by erosion

processes. Some scientists consider the exposure of the rock by isostasy. This is a useful term in

earth science and is understood as the vertical positioning of the continental crust, maintaining

balance of gravitational and buoyant forces. Like a ship, which submerges more or less

depending on whether it is loaded or empty, the crust’s vertical position in the mantle also

depends on its density. To maintain isostatic adjustments the lightened mountain is buoyed up as

erosion takes away its top material. As result, the submerged portion of the continental crust

(standing as mountain) is raised to shallower depths.

There is another group of rocks that constitute the Earth’s crust. These are called

metamorphic rocks. When pre-existing rocks, such as sedimentary rocks and/or already

crystallized igneous rocks are subject to increased temperature and pressure we get metamorphic

rocks. The high T and P conditions come from deep burial during mountain building processes.

Metamorphic rocks are characterized generally by layers and band of minerals called foliation.

Metamorphism also produces non-foliate rocks like marble and quartzites. Different

combinations of T and P result in different grades of metamorphism characterized by minerals:

chlorite, biotite, garnet, staurolite, kyanite and sillimanite---in increasing grade. When the main

agent of metamorphism is T we address this as contact metamorphism in contrast to dynamo-

thermal or regional metamorphism that is associated with mountain building processes. When

hot water during metamorphism transforms the effected rocks, we get hydrothermal

metamorphism which is often associated with valuable ore deposits of copper, zinc, lead, gold

etc. The study about all these three types of rocks is the subject of Petrology.

The formation of all these three types of rocks, whether igneous, sedimentary or

metamorphic rocks, has happened many times in the Earth’s history. And it becomes a task for

geoscientists to decipher the geological history in rocks as if the man has travelled back in time

to view the geologic processes. This history is recorded only in the rocks and the fossils

contained in them. To use a rock to read Earth’s history, it is important to know how old the rock

is. Today we use radiometric dating of rock for actual age. But before this, geoscientists relied

upon the relative dating. Relative dating is the ordering of rocks in sequence (depositional order

of old vs. younger) on the basis of comparative ages. Relative dating considers several basic

principles.

1. Horizontal deposition: Each layer of sediments is laid down nearly horizontal over

older sediment. Layers that are inclined at any angle were tilted into the positions by

tectonic disturbance such as uplift or folding, after they were deposited.

2. Superposition: In an undisturbed (flat) sequence of sedimentary rocks, each layer is

older than the one above and younger than the one below (called Law if

superposition), like a huge cake.

3. Cross-cutting: A fracture or Fault that cuts into rock must be younger than the pre-

existing rock. Similarly, an igneous intrusion (an intruding magma) is younger than

the rocks into which it intruded.

4. Inclusion: is piece of rock contained within another rock. Any inclusion is older than

the rock containing it.

5. Faunal succession: The evolution of life is documented in the rock record in the form

of fossils. Because fossilized organisms follow one another in a definite time

sequence (Darwin’s evolution theory on which paleontology as the science of fossils

is based), it is possible to identify the relative age of a rock from the fossil contained

in it. It is also interesting that fossils become a great tool for matching up rock of

similar ages in different regions.

Once geologists establish a time period on the basis of fossil record, the fossils can be

used in the rocks to identify other rocks of the same age in distant regions of the Earth. This is

the subject of stratigraphy. Thus time related changes in fossils could be used to erect a

stratigraphic time scale. Many of these concepts go back to the 18th

century geologists, especially

William Smith who is regarded father of stratigraphy. The reconstruction of geological history

considers the concept that present is the key to the past. The natural things which are happening

now may have also occurred in a similar way in the geological past.

2.6 Record of Earth’s early history

The Earth has witnessed a large number of events from its existence since about 4.6

billion years ago. This vast time span is called geologic time. The oldest time period is called

Hadean (4.5 to 3.9 billion years) is followed by Archean which ended at 2.5 billion years.

Geologic history of these early periods is not very well known as the rocks were formed mostly

from lava (magma) and were overprinted by thermal effects of later eruptions. Moreover, life

also did not appear on the Earth until mid Archean time.

Life on the Earth appeared late because early atmosphere was dominated by CO2, N2O,

SO2, NH3, N2, and H2O vapour. There was no free oxygen in the early atmosphere until Late

Archean time which is evidenced by unicellular chlorophyton, called Cyanobacteria. These

single-celled algal organisms or Cynaobacteria, existing as earliest life, entrapped sedimentary

grains and formed sedimentary layer of fossilized Cyanobacteria, called Stromatolytes. These

fossils are of 3.5 billion years age and are found in Western Australia. This is the first direct

fossil traces on the Earth, and thus in support of oxygen in the early Earth’s atmosphere. The

oceans of Late Archean and of immediate later age could have been full of the algal mats

because we find stromatolytes elsewhere in the periods of 2.5 billion years to 570 million years.

For the origin of oxygen, it is proposed that Cyanobacteria produced oxygen (O2) as a by-product

of photosynthesis:

CO2 + H2O (in light) → CH2O (carbohydrate) + O2

Biochemists claim that prior to photosynthesis, atmospheric oxygen was produced by

photochemical reaction in which UV rays dissociated Earth’s water:

2H2O = 2H2 + O2

The oxygen produced by photosynthesis and photochemical reaction helped to develop

and support multicellular life and also ozone layer to protect life from dangerous solar radiation;

free oxygen was necessary to build ozone layer.

2.7 Geologic Time

Geologists use a time scale in million years. They have divided the time span in time

units of different sizes. The largest unit of geologic time is called the eon. The eon we are living

in is called the Phanerozoic which means visible life. The Phanerozoic eon begins from 550

Million years (abbreviated Ma, milliard anno in Latin) until present. This eon is further divided

into 3 eras: The Paleozoic era (time of ancient life); The Mesozoic era (the time of middle life);

and the Cenozoic era (time of recent life). Thus, the Cenozoic is age of mammals. The

geological time scale is shown in Table 2.

The eras are further divided into smaller time units called Periods. Periods are

characterized by differences among life forms. Finally, periods are divided into the smallest

geological time, the epoch. Epochs are generally defined in terms of geological distinctions

rather than differences among life forms. The names in the geological column are interestingly

derived from rock types (see Table 2). Carboniferous from coal strata; Cretaceous from chalk

strata. Others come from where they were first described: Jurassic from Jura Mountain.

Permian (Perm) in Russia. Cambrian is after Latin word for Wales, while Ordovician and

Silurian get their names from ancient Wales’s tribes. Devonian after Devon in England.

Triassic is so called because it divides naturally into three subunits (not shown here).

Note that Phanerozoic makes up only about 11% of Earth’s history while majority of the

Earth’s history occurred in Precambrian, before Phanerozoic era. This vast span of time, over 4

billion years, is divided into three eons, as stated already and reproduced here for ready reference

Hadean (4.5 – 3.9 Ga, giga anno)

Archean (3.9 – 2.5 Ga)

Proterozoic (2.5 Ga to 550 Ma).

Together, the three ancient eons make the Precambrian time (4500 to 550 Ma).

The Precambrian time makes up about 90% of the Earth’s history, but we know the

least about this geological time. Most of the rocks that were formed in the early period of Earth

have been eroded away or metamorphosed or even recycled into the Earth’s interior. The

beginning of the Precambrian was marked by considerable volcanic activity and frequent

meteorite impacts. During Hadean eon (4500 – 3900 Ma) large chunk of interplanetary debris as

a leftover of the formation of the Solar system continually smashed into the Earth. At this time

the Earth was an oceanless planet covered with stuff (lava streams and gases) from volcanic

eruption from hot interior.

In the Archean time there was already a permanent crust as evidenced from the

radioactive dating of the continental nuclei in some regions of the globe. The early formed

continental crust was patchy but later these continental fractions or microcontinents joined to

form bigger landmasses, which we now call continents. The oldest part of the continents is called

craton that is made up of granite-like rocks. Most of these cratons are buried beneath

sedimentary rocks. But deep erosion has exposed rocks of cratons. This exposed cratonic region

is called the shield, e. g. Indian shield, Canadian shield etc. The continents or landmasses again

fragmented and moved as lithospheric plates due to mantle convection currents. The assembly

and reassembly of the plates constitute the domain of plate tectonics, discussed later.

The Phanerozoic eon has been very interesting period, although it makes only 11 % of

the Earth’s history. Here, a variety of life, as fossils, is found in the rocks of this time, unlike the

Precambrian which contain too few species to allow any detail information. As stated, the

Phanerozoic is divided into 3 era.

The Paleozoic era (ca. 550 - 251Ma) lasted for about 300 Ma. Just before the dawn of

this era, the continents were joined in a single supercontinent, called Rodinia (Russian word for

―homeland‖). Early in the Paleozoic, the supercontinent Rodinia fragmented. Consequently sea

levels rose and fell several times due to movements of plates and consequent disturbance in

oceanic currents. This allowed shallow seas to cover the continents periodically (geologically

called marine transgression), causing deposition of sediments on coastal regions and inland of

the continents. It also influenced the development of life forms, especially marine life (fishes,

amphibians and reptiles). The Paleozoic era is divided into 6 periods; each is characterized by

changes in life forms and tectonics.

The Cambrian Period (ca. 550 - 488 Ma) has a stretch of 50 million years time between

two ice ages, one in the Late Proterozoic and the other in the Early Ordovician. So Cambrian

itself was a warm period, implying that one of the continents were located at the poles during

Cambrian. Ice sheets and glaciers that had formed during the Proterozoic melted during the

Cambrian, resulting into sea-level rise. Low-elevation areas were flooded and much of the land

became covered by seas. The flooding expanded habitat for the marine invertebrates that had

first appeared in the Paleozoic. These organisms thrived and produced a great diversity of

marine organisms. Hence, Cambrian period became known as the ―Cambrian explosion‖ of

species---an event in the Earth’s history in which life suddenly became far more common and

varied. The most important event in the Cambrian was the evolution of organisms that had the

ability to secret calcium carbonate (CaCO3) and calcium phosphate (CaPO4) for the formation of

outer skeleton or shells. Skeleton gave protection against predators and UV-rays, allowing

organisms to move into shallow habitats. The most diagnostic animal of the Cambrian is the

trilobite—the armored ―cockroach‖. The trilobite lived well beyond the Cambrian period. There

are also soft-bodied creatures in Cambrian as found in Burgess Shale in Canada.

The Ordovician Period (488 – 444 Ma). This was a cold period because most of the

landmasses had aggregated near the South Pole. The Ordovician marks the earliest appearance of

vertebrates, including the jawless fishes. Because of glaciations, sea levels dropped,

consequently the shallow-water organisms were deprived of their habitats. This is marked by

extinction of shallow water marine fauna, while deep water life remained unaffected. The

appearance of first primitive fish and the now extinct marine organisms seen as saw-tooth like

fossils, called graptolites, are characteristic of the Ordovician.

The Silurian Period (444 – 416 Ma). During this period, most of the landmasses

remained near the S-pole. However, North America and Europe were positioned near the

Equator. This is evidenced by the deposits of rock salt and other evaporite minerals. This period

is marked by the emergence of plants on land. Concurrently, there were also many shallow-water

life forms such as corals and fresh-water animals. Also, air-breathing scorpions and millipedes

were common land animals during the Silurian.

The Devonian period (416 - 359 Ma). The massive sandstone deposits, known as the

Old Red Sandstones, are characteristic of this period. During the Devonian, North America and

Europe drifted near the equator whereby the climate was warm and moist. Therefore, plants had

spread over the land surface, with many more species of fish and growth of plants and insects. In

the seas, fishes diversified in many new groups, which is why Devonian is casually known as the

―age of fishes‖. Among the bony fishes, the finned fishes gave rise to land-living terrestrial

vertebrates which shared many features with the amphibians of today. Remember that during

Devonian the Gondwanaland continents, namely India, Africa, South America, Antarctica and

Australia remained in the Southern hemisphere. The end of Devonian was marked by a mass

extinction of many marine species. Its cause is still unknown.

The Carboniferous Period (359 – 299 Ma). This period is marked by warm, moist

climate and hence contributed to lush vegetation, forests and swamps. As plants and trees dies,

their remains settled to the bottom of these stagnant swamps and decayed an aerobically to

produce coal. Most of the coal used today derives from these Carboniferous swamps. In this

period, insects evolved to diverse forms such as cockroaches, dragonflies etc. It was during the

Carboniferous period that the Appalachian mountain of eastern North America was formed when

the united Europe-North America (together called Laurasia) collided with the Gondwanaland.

North Americans divide the Carboniferous into Lower (Mississippian) and Upper

(Pennsylvanian) units.

The Permian Period (299 – 251 Ma). This was the period when Wegener’s Pangaea was

formed, with all the land we see today. The beginning of Permian has many signs of life that may

have continued from Carboniferous. This was the period when reptiles and ancestors of

mammals were evolved. The end of Permian is marked by much mass extinction, what is known

as the Permian extinction—the biggest mass extinction in the Earth’s history. Permian extinction

causes the demise of 90% of species living at that time. The cause may have been a reverse

greenhouse effect due to lack of CO2 in the atmosphere when so much life was converted into

coal. The other cause may be that there was huge volcanic eruption at that time. As result,

sulphate aerosols from the eruption could have rapidly cooled the climate by blocking solar

radiation. Because of these two causes together, the photosynthesizing species may have been

the first to be affected, breaking the entire food chain and hence causing mass extinction. It is

also possible for this major extinction that the formation of Pangaea generated changes in the

temperature and sea level, leading to the Permian mass extinction.

Extinction of a species can occur only of its habitat is destroyed or the prevailing

environmental conditions suddenly change in such a way that populations is unable to adapt.

The end of the Permian is also the end of the Paleozoic era which showed so many

changes to life on the Earth through time.

Mesozoic Era (251 – 65 Ma). The Mesozoic Era is known as the ―age of reptiles‖.

Reptiles that survived the Permian extinction became dominant species of the world in this era.

Mammals also evolved in early Mesozoic but they were relatively small compared to the

dinosaurs. Land plants also diversified during this era. The major geological event of the

Mesozoic was the breakup of the landmass Pangaea which existed 200 Ma ago. Rifting of

Pangaea began in Triassic, continued in Jurassic and by mid Cretaceous the break up had split

into several smaller continents. The breakup of Pangaea impacted biological evolution.

Organisms were separated from one another and caused divergence in the evolution.

The Mesozoic starts with Triassic period which lasted from 251 to 199 Ma ago during

which map of the world did not change much. The ancestors of both dinosaurs and warm-

blooded present-day animals gained ground at this time. The Jurassic (199 – 145 Ma) has the

fossils of corals and other animals, indicating warm climates. The first bird Archeopteryx also

dates from this era. The Jurassic saw the final breakup of Pangaea. North and South America

were separated by a seaway. India also separated from the East Gondwana assembly. Antarctica-

Australia remained joined. At this time the sea level rose up and previous land was flooded. The

final period of Mesozoic is the Cretaceous Period which lasted from 145 to 65 Ma ago. The

high sea levels had vast chalk (limestone) deposits across large areas of the world. Cretaceous

was also the time when huge volcanic outpouring occurred. Deccan basalts of India are well

known and are found around large part of Maharashtra state of India, particularly in and round

Mumbai. Dinosaurs and other animals disappeared in this period. What caused the Cretaceous

extinction is again a puzzle. Some say huge volcanism, others claim huge meteorite fall. But

break up of Pangaea resulted into sea-level rise and also change of habitat for the dinosaurs and

other animals.

The rest of the geological column is the Cenozoic era. Its lower half, called the Tertiary,

is itself divided into Paleogene (65 -23 Ma) and Neogene (23 to 1.8 Ma). Enormous tectonic

disturbance occurred throughout the world during the Tertiary. There was further opening of the

Atlantic Ocean in the Paleogene. This was associated with further movement of continents. And

Africa-Arabia collided with Europe to raised Alps while India and Asia collided to form the

Himalaya. Major evolution of land is marked by the development of mammals. The Neogene

period lasted for about 21 million years time. This period is noted for the separation of human

ancestors from their last ape relations. The Neogene is divided into older Miocene and younger

Pliocene. The boundary is defined by the percentage of still-existing molluscs in fossils.

The final phase of story is the Quaternary period which lasted just 1.8 million years

ago. In the geological nomenclature it has been named the Pleistocene period. This is too short a

period to have something happened as a global event. It is marked by the formation of most

landscapes of northern hemisphere through a number of glaciations. During the Pleistocene

epoch global temperatures dropped and ice age occurred. The cool temperature had profound

effect on life, particularly in their adaptation, developing wooly coats on animals. Because of the

cold of Pleistocene sea levels were lowered and which made the migration of Homo sapiens

easier. For example, the ice-made ―land bridge‖ (now the Bering Strait) between Siberia and

Alaska provided easy migration route for the Homo sapiens from Asia to North America.

The time we are living is called the Holocene (10,000 year to present). Some cold

climate periods occurred as between 1200 and 1700 AD. But the Holocene is a relatively warmer

period. The present time has been warmer than an ice age. It is referred to as interglacial period,

perhaps because the pessimists, in-charge of the terminology, think that the warm period is a

prelude to the next ice age. It is possible that global warming may also force humans to migrate

to colder regions of the Earth. But we leave this to the fate of the human race!. The Earth has

interesting interaction with the Sun and we have to look on this aspect now.

2.8 Sun-Earth-Moon Interactions

The Sun-Earth-Moon forms a dynamic system that influences all life on the Earth. The

Sun is 109 times larger in diameter than the Earth. On the other hand, the Earth is about 3.4 times

larger in diameter than the Moon. The distance between the Earth and the Moon is 3,84,000 km

while the Sun is nearly 400 times (15,3600,000 km) away from the Earth.

The Earth spins W to E on its axis and causes day and night. This can be inferred simply

by observing the Sun rise first in Japan and thereafter in India to the west of Japan. Scientists

used other methods for this anticlockwise rotation of the Earth whereby the Sun appears to move

E to W each day. It is every day experience that we observe while standing on the Earth a daily

rising Sun in East and setting of the Sun in West. Remember that this is only apparent or illusory

because Sun does not revolve around the Earth. It only appears that way because we observe the

sky from the planet Earth that rotates. One complete rotation of the Earth defines one year,

precisely 365 days and 6 hours. Because of the Earth’s revolution the Sun also appears to move

N and S in the sky; northward during the northern summer and southward during the northern

winter.

The Sun, being in the centre of the solar system, affects the Earth interestingly. The Earth

receives heat or light from the Sun, at the rate of 340 Watts for every square meter surface. This

energy is not equally distributed around the Earth because the Earth’s orbit around the Sun is

tilted at an angle 23.5 degree to the equator. That is why all globes in the market have a tilt of

23½ degree to the horizontal. A consequence of this tilt off a vertical axis we have seasons--

summer, spring, autumn and winter. Earth’s axis remains tilted at the same angle as it orbits the

Sun. It points once toward the Sun and once away from the Sun. Seasons have nothing to do with

the Earth’s distance from the Sun since its orbit varies only slightly (1.7% from a perfect circle).

The Earth’s orbit is therefore only slightly elliptical. With its elliptical orbit and 23.5o tilt, the

Earth is closest to the Sun on 21st June, called Summer Solistice and also farthest from the Sun

on 22nd

December, called Winter Solistice. The first day of the Summer Solistice is the longest

day of the year as the North Pole is of the Earth is closest to the Sun. For a person standing on

the 23½ o north latitude, the Sun would be at zenith (Sun’s maximum height) on the summer

solstice.

If the Sun is higher in the sky, it heats by shinning down on the Earth below rather

steeply, like shining a torch straight on a wall. If we shine the torch at an angle, the light is less

brighter. This is because the same amount of energy in the former case is hitting smaller area.

The Sun rays are directly vertical on the equator twice, around 21st March and 23

rd September.

These are called Summer Equinox and Winter Equinox. On these times, the days and nights are

of equal length.

Like the Sun appears to change its position in the sky throughout the year, in a similar

way the Moon also changes position as it orbits the Earth. As the Moon orbits, its illumination

side changes. The sequential changes in the appearance of the Moon is called Lunar phases. We

know that the light given off the Moon is a reflection of the Sun’s light. Moon is illuminated at

all times. But only one-half of the Moon is illuminated. How much of this lighted half is visible

from the Earth varies as the Moon revolves around the Earth. When the Moon is between Earth

and Sun, the side that is illuminated is not visible. This is called new Moon. But as it moves in

its orbit around the Earth, more of the Sunlit side of the Moon is visible. So when the Moon

moves to the far side of the Earth from the Sun, we have full Moon, with entire Sunlit side facing

the Earth. The length of time it takes from the Moon to go through a complete cycle, from one

new Moon to the next is called Lunar month. It is equal to 29.5 days. This is larger than the 27.3

days it takes for one revolution around the Earth. The Moon also rises and sets 50 minutes each

day because the Moon moves 13o in its orbit over a 24 hour period. The Hindu calendar is based

on the Lunar movement and its days become shorter or longer and the Calendar is adjusted

accordingly.

2.8.1 Earth tides

We know that the Sun contains nearly all the mass of the Solar system. As a result it has

all of the gravitational pull and this keeps the Earth (and other planets) in its orbit. The Moon

also has gravitational pull which is more powerful than that of the Sun, because of its small

distance from the Earth. The gravitational pull of the Sun and Moon gives rise to tides---the rise

and fall of ocean water. The gravitational attraction of the Sun and Moon also raises detectable

tides or bulges in the atmosphere and in the solid Earth itself. But the air tides are much smaller

than the variation in the Earth’s atmospheric pressure (see chapter 4). Bulges in the solid Earth

is almost negligible but the US and Japanese scientists claim that when the Solar and lunar tides

coincide, a significant earthquake or volcano may ensue. It is the tides in the ocean that are most

noticeable to humans and other life on the Earth. These tides are interesting. The basic shape of

ocean tide is a bulge toward the Sun or the Moon. The Moon raises a tide of about 1 meter high

at the Earth’s equator, while the Sun produces about ½ meter. This may not be much in the Earth

with 12700 km diameter.

When the rotating Earth is stretched along the line joining the Earth’s center to the Moon

and the Sun. we get two bulges in the oceans (as well as in atmosphere and the Earth itself).

Hence we get two tides a day. The sun tides are 12 hours apart, but the Moon tides are about 12

hour and 25 minutes apart, because of the Moon’s movement around the Earth, as stated earlier.

We have spring tides when the Moon is nearest to the Earth and the Earth is nearest to the Sun.

When the Moon is at right angle to the Sun and Earth line, we have neap tides. So the height of

the tide depends on whether the gravitational pull is working together or in opposite direction.

The consequence of the tide is very interesting. It has been steadily slowing down the

rotation of the Earth. Calculations showed that days are getting longer by about 1.4 milliseconds

(1/1000 second) every century. This may not sound much but it adds up. And about 550 million

years ago it gives 420 days in a year with each day 21 present-day hours in length. How did we

know this is indeed interesting? In a fossil shell of Cambrian (550 million years) age people

counted about 400 annual rings, in a similar way as we count growth rings in a circular section of

a tree-trunk. We know that trees like summer more than winter and they grow when it is warm

and therefore the age of a tree can be determined by counting growth rings. There are also

creatures which show monthly growth rings. Paleontologists now study corals that form solid

shells in the day light but stop at night. Between one day growth and next day we get a small

band which can be observed with a microscope. The sedimentologists use lake deposits to find

out the chronology of the past. When the snow melts, spring floods give large amount of mud

which is deposited into the lakes as dark layer of coarse sediments. Above these is layer of fine

sediments deposited on the later in the year when water was very calm. This type of layering is

called varve clay—a pair of light and dark sediment layers. Like counting tree rings we can use

the varve to build up lengthy climate records.

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Chapter 3

Hydrosphere, our Blue Earth

3.1 The oceans

The solid Earth is overlain by the oceans which occupy about 70% Earth’s area. The

ocean water is about 97% of total water found on the Earth. Another 3% as fresh water is

contained in landmasses. The water on and in the Earth’s crust makes up the hydrosphere

(hydro means water in Greek). Some people call the frozen belts at the Polar Regions as

cryosphere. We shall also talk about it in this chapter. The ocean water looks blue from space

because blue light is reflected while other wave lengths of the visible spectrum are absorbed by

water. Scientists suggest that oceans existed since the beginning of the Earth’s history because

detritus zircons of 4.4 billion years old (Earth is 4.6±1 billion years old) in a conglomerate from

Western Australia and glassy crust on ancient lavas show the evidence of having contacted

water. Scientists hypothesize that the ocean water originated from two sources. One is remote

source, when comets and asteroids containing 0.5% water collided with the Earth and left behind

much water to fill in the Earth’s vast hollows. Another hypothesis is that volcanism from the

Earth’s interior contributed water, besides gases and other products. The volcanism took place

over the course of several hundred million years. Over time when the Earth’s surface cooled, the

water vapour gradually condensed and fell as rainwater on the Earth’s surface to collect in the

large hollows and low regions of the Earth, which we call oceans.

Out of the 71% oceanic areas, 81% water covers the southern hemisphere while landmass

dominated northern hemisphere has only 61% water. There are 3 major oceans: Pacific Ocean,

Atlantic Ocean, and Indian Ocean. The Pacific Ocean is the largest than all landmasses

combined. Atlantic Ocean extends for about 20,000 km from N of Arctic, where it is called

Arctic Ocean, to Antarctica in the south. Indian Ocean is located in the southern hemisphere. The

storm-lashed region surrounding Antarctica is known as the Southern Ocean. All the oceans are

interconnected but the different oceans are only for historic and geographic reasons.

Polar regions are covered by vast ice cap which is very thick and is called pack ice. The

percentage of ice on the Earth has varied over geologic time from zero to as much as 10% of the

present hydrosphere.

The level of ocean surface is known as the sea level. The sea level has risen by several

meters when ice melted during warm periods and fallen by hundreds of meters when glaciers

expanded during ice ages recorded a couple of times in the Earth’s history. Tectonic forces also

affect sea level for example when the Earth’s crust is uplifted or sunken. Scientists found sea

level rise by about 3 mm per year between 1994 and 2004, mainly due to thermal effects.

3.1.1 Composition of Ocean water

The ocean water contains dissolved gases (CO2, O2 etc.) and dissolved nutrients, mainly

nitrates and phosphates, besides containing mineral salts in solution. More than 70% chemical

elements are found in it , but sodium chloride (NaCl) plus four other salts, magnesium chloride

(MgCl2), sodium sulphate (Na2SO4), calcium chloride (CaCl2), and sodium fluoride (NaF), make

up 97% of the salt in the sea. The oceans are therefore saline, too sour to drink. The salinity is

understood as the proportion of dissolved salts to pure water. Oceanographers express salinity of

the ocean water in grams of salt per kilogram of water, or part per thousand (ppt). Average

salinity as 35 parts per thousand or 35 ppt. Scientists note this with the symbol ‰ (per mill). So

the salinity of the ocean is written as 3.5‰. Remember that the salts in ocean water exist as ions.

In terms of concentration of ions, sea water is about 55% Cl-, 33% Na

+, and 8% SO4

-2. Each of

the other ions makes up 1% or less of the weight of a given sample of sea water.

Salinity of sea water varies in a narrow range. Decreases when freshwater are added, as

during heavy rain or when ice melts on a seasonal basis. Conversely, salinity increases with

evaporation. It is for this reason that in equatorial regions where rains are abundant, salinity is

lower (~32 ppt). In polar regions, salinity increases because of ice formation, making the leftover

water more salty. Therefore explorers use the ice for drinking. In summary, the salinity increases

as you travel N or S toward higher latitudes. The lowest salinity occurs where large rivers empty

into oceans, creating areas of water called estuaries, formed by reverse condition to delta. The

sea water in tropic is saltier because more water evaporates from the sea at high temperatures.

Water in the 1 – 3% salinity is termed brackish water. If the salinity goes over 4%, the water is

termed hypersaline, e.g. Dead sea, which is filled by rivers but it empties only by evaporation so

the salt stays, with no outlet..

The oceans seem to be saline from very ancient time. This is inferred from the

proportions of Mg and Ca in carbonate shells of ancient marine organisms. And the reason for

the salinity is that salts have been added to sea water by volcanic eruptions and by weathering of

rocks. On the other hand, salts are removed from sea water by biological processes (silica by

diatoms, & Ca-salts by foramanifers) and formation of evaporates. When marine organisms die,

they sink and their hard part becomes the component of bottom sediments. Decay of the

organisms finally releases salts. Thus, we see that salts are added to, and also removed from, the

oceans, keeping the salinity of ocean water nearly constant, near 3.4 permil. It seems that the

marine life is responsible for this constant salinity (3.45 ppt or 3.45‰) for their own survival.

The presence of various salts results into different physical properties of ocean water

from those of freshwater. Because of salts, sea water is denser, or has higher density in language

of physics. A similar difference in physical properties occurs due to temperature. The ocean is

heated from above by the Sun. The surface layer thus becomes hotter than rest of the ocean. But

oceanic surface temperature ranges from minus 2 degrees (-2oC) Celsius in Polar waters to 30

oC

in equatorial regions, with average temperature of surface being 15oC.

3.1.2 Ocean water layering

Below the surface layer of the ocean is the mixed layer up to about 200 m down where

wind, tides and currents try to homogenize the physical properties of ocean water.

Oceanographers noted that from 200m depth the T begins to fall steeply to about 4oC, in a layer

called thermocline. The thermocline is a transition layer characterized by decreasing

temperature from 100 to 1000 m depth. Below the 1000 m layer is a dark, cold layer with

temperatures near freezing. This deep ocean water is always cold, even in tropical oceans.

Because of dissolved salts the ocean water at this great depth is dark since sunlight can hardly

penetrate. Interesting to note is that at thermocline red light does not penetrate as far as the blue

light. So, most marine organisms to their advantage have shades of red on their body so as to

appear black and escape from predators.

The ocean layering is based on density differences. The density of sea water varies from

1.02 to 1.03 g/cm3 against fresh water having density 1 g/cm

3. Density of ocean water varies due

to salinity and temperature variations. Density variations due to salinity are far outweighed by

temperature variations. Oceanic water freezes below zero degree at -2oC) while fresh water in

your fridge becomes ice at 0oC. Salinity and T seem to have opposite effects on density. As the

salinity goes up and its T drops, the oceanic water increases in density. Although the density

variation in ocean water is small it is an important factor in circulation of ocean water.

In Polar Regions, frozen sea water overlies the saltier cold water, because salt ions are

not incorporated into ice crystals. This saltier cold water sinks and migrates toward equator as

deep water mass along the ocean floor. On the other hand, subtropical waters in winter time

move into Polar Regions where it becomes colder and denser than surrounding polar surface

waters. The result is that the moving subtropical water sinks, (since warmer, less dense water

floats on the cold water). Oceanographers recognized three deep-water masses, mentioned below

in order of decreasing density.

1. Antarctic Bottom Water, moving westward toward the equator

2. North Atlantic Deep Water moving towards east

3. Antarctic Intermediate Water, moving westward

As stated, the movement of Deep Ocean water results from difference in density and temperature

between water masses. Density currents move slowly in deep ocean waters and follow a general

path—the Global Conveyor Belt. The conveyor belt begins when cold, dense water such as

North Atlantic Deep Water and Antarctic Bottom Waters sink at the poles. After sinking, these

water masses slowly move away from the poles and circulate through major ocean basin. After

hundreds of years the deepwater returns to the surface through by vertical movement called

upwelling that originates below thermocline. Once at the surface, the deep water is warmed by

solar radiation. All the three major deep waters, stated above, occur in Atlantic Ocean, but Indian

and Pacific Ocean contain only two Antarctic deep water masses.

In contrast to the slow movement of deep water currents, moving with density differences

between water masses, the surface water movements are largely driven by the wind and by the

Coriolis force due to varying rotational velocity from the equator to the poles of the Earth.

Therefore the top of 100 to 200 m of the ocean moves at a speed of more or less 100 km per hour

when the winds move the water along with it. We know that Trade winds in northern hemisphere

blow from E to W (Earth spins W to E), so the ocean currents also flow from E to W in tropics.

Northern Polar winds also push surface currents form E to W in the northern hemisphere. But

due to Coriolis force the currents are deflected toward E in the northern hemisphere and toward

W in the southern hemisphere.

3.1.3 Oceanic currents

If the Earth had no landmasses, the global oceans would have simple belts of Easterly and

Westerly surface currents, in closed circular current systems. But the Earth has land masses,

more in northern hemisphere than in southern hemisphere. So, the ocean currents are divided into

several belts, called gyres. In each gyre the currents in northern ocean are west moving due to W

to E rotation of the Earth. When the currents encounter landmasses, they are deflected toward the

poles. These Poleward-moving waters carry warm, tropical waters into higher and colder

latitudes. An example of a warm current is the Gulf Stream in North Atlantic, which flows (170

km/Day or 2 m/second) from the Gulf of Mexico to Western Europe. By the time this westerly

current or Stream reaches the west coast of NW Europe, where it is called Atlantic Drift, the

warm water has cooled and deflected by landmasses to return to the Equator. The resulting

current then brings cold water from higher latitudes to tropical regions. This is the Californian

Current in eastern Northern Pacific. Also, in north Pacific, the Kuroshio Current of Japan carries

warm waters northward and the Californian current brings it southward again. Thus there are two

gyres (currents) in the northern hemisphere: the Northern Pacific gyre (moving W to E) and the

Northern Atlantic gyre (W to E movement). In the south Atlantic we also have Brazil current and

Agulhas in the Indian Ocean, both having westerly currents.

In the southern hemisphere, the oceanic current flows non-stop by wind and waves from

W to E. The gyres of southern hemisphere circulate in anticlockwise direction. There are three

gyres in the southern hemisphere. These are the southern Pacific gyre; South Atlantic gyre and

the Indian Ocean gyre. The parts of all gyres closest to equator move toward W as equatorial

current.

This is the rough outline of the general circulation patterns of the surface ocean current,

leading to the distribution of heat, salt and nutrients from one region of the ocean to another.

These ocean currents can be tied with the climatic circulations, and meteorologists face tough

time for accurate weather forecast.

More than for its water, the ocean has attracted oceanographers for its hidden topography.

When we move into the sea from shoreline—the place where ocean meets the land—we see

sand, familiarly known as beach sand. It is loose sand formed from shore erosion by wave action.

There is also bigger size eroded material, depending on the energy of the wave striking the coast.

Several types of erosional features can be seen in coastal areas. These include Spit (a narrow

bank of sand), Mainland beach, lagoons, Baymouth bar (closing of Spit), Barrier islands (long

ridges of sand), etc. The edge of the continent covered with sediments is the continental

margin, but continents extend further inside the ocean. Shallow part closest to the continent is

the continental shelf. It is a nearly flat underwater surface, extending from the shoreline toward

the ocean basins. It generally extends seaward to a width of up to ~1500 km with a depth of 130

m sea water. You can guess the situation if you are told that the sea level during the last ice age

was 130 m lower than at present.

Beyond the continental shelves, the sea floor drops quickly to depths of several km, with

a slope of about 100 m/km. These sloping regions are called the continental slopes. The

continental slope is considered the true edge of a continent. From here onwards starts the oceanic

crust. In many places the slope is cut by deep submarine canyons, comparable to Grand Canyon

in Arizona. At the base of the continental slope there occurs a wedge of sediments which were

brought from shelf and slope region by rapidly flowing water currents along the bottom of the

sea, called turbidity currents in geological term. Scientists study turbidity currents in laboratory

by simulating them in glass tanks. The gently sloping deposits at the base of slope are several km

thick and are called continental rise. The rise become thinner and eventually merges with

sediments of the ocean floor.

Beyond the continental margin are ocean basins which are generally 3 to 5 km deep from

surface and are characterized by flattest and deepest part of the ocean floor, called abyssal

plains. These plains are covered with fine sediments and sedimentary rocks on top of ocean floor

basaltic rocks.

During World War Second and perhaps because of this World War, scientists started

exploring the ocean. They used a variety of research vessels to learn about the topography, water

depth, chemistry etc. of deep oceans. Echo Sounding methods or Sonars from a ship were used to

map the ocean floor. Sometimes vessels (submersibles) carried humans in them to collect

samples of sediments, water and biological material. While other vessels e.g. Autonomous

Benthic Explorer, ABE, without pilot made video recording of the deep sea environment,

temperature and water chemistry while Remotely Operated vehicle, ROV, were deployed from a

ship to collect deep sea data, as deep as 6000 m. And the findings were very interesting. The

most prominent features of the oceans are Mid Oceanic Ridges (MOR) which run all through the

ocean, with a total length of 65,000 km---a distance greater than Earth’s circumference. The

MORs have an average height over 6 km and emerge from the ocean as volcanic island. The

MORs are the sites of frequent volcanism and earthquake activity. The crest of these Ridges

often has valleys called Rifts that run all through the centre of the ridges. The MORs do not run

continuously as they are dissected by stepped fractures, which are about 60 km wide and curve

across the sea floor. Another interesting feature is the deep-sea trenches. These are elongated

depressions of about 100 km width. The trenches extend a few thousands of kilometers.

Satellite data have revealed that the ocean floor is dotted with several solitary mountains

called seamounts. They are not located near the active volcanoes and are therefore considered as

being extinct volcanoes.

3.1.4 Ocean features

Many people in scientific community had considered oceans and continents as permanent

features. But a German meteorologist, Alfred Wegener, impressed by the geometrical fit of

Africa and South America on map, thought that the two continents were once united but later

drifted in their present position. He gathered a variety of evidence including fossil flora and

fauna, climatic indicators (coal, glacier deposits etc), trends of geological structures across

continents, similarity of ages of rocks at margins of the now widely separate continents. Based

on these evidence he suggested that all the present continents had assembled 200 million years

ago into a supercontinent which Wegener called Pangaea. Wegener then proposed that the

Pangaea subsequently broke up and the continents drifted slowly in their present position on the

globe. But geophysicists rejected Wegener’s hypothesis because there was no mechanism known

to geophysicists to move the huge continents. For the rest of his life, Wegener continued

travelling to remote and difficult regions to gather evidence in support of his theory. While

collecting further evidence he made an expedition to Greenland in 1930. But he died of

exhaustion and his body could not be recovered by his fellow explores who called off the

expedition.

Oceanographers continued their research. They collected samples of deep sea sediments

and the underlying oceanic crust. Analyses of these sediment and rock samples led to two

important discoveries. First, the ages of the rock that made up the ocean floor varies such that

samples near the oceanic ridge were younger than the samples collected away from the ridge.

This trend showing oceanic crust younger near the ridge and successively older away from the

ridge was found symmetrical across the ridges. Scientists also discovered from the rock samples

that rocks of the ocean floor are not older than 180 million years. Why is the ocean floor rocks

are so young whereas the continental rocks are very old—some are at least 3.8 billion years old.

This was a great puzzle to the scientists, because geologists accepted that ocean has existed

nearly the same time as the rocks had appeared on the Earth’s crust. It was a big question as to

why there was no trace of older oceanic crust.

The second discovery was that ocean floor sediments are only a few hundred meters thick

at the most, whereas the continents have sediment blanket of as much as 20 km thick. Scientists

also found that sediments near the oceanic trench were found thicker than at any other place on

the ocean floor.

To solve these puzzle, scientists performed paleomagnetic studies (fossil magnetism) of

the rock samples. We know that when lava solidifies, iron-bearing minerals such as magnetite

crystallize like a tiny compass and align with Earth’s magnetic field. We know that Earth’s

magnetic field is reversed when the flow of molten iron in the Earth’s outer core changes. This

would cause compass to point to the South, instead of N when the magnetic field is normal as at

present time. The basaltic lavas of the ocean floor were investigated for their fossil magnetism.

When scientists towed magnetometers behind a ship to measure magnetic orientation of rocks of

the ocean floor a surprising pattern emerged. The rocks parallel to the ocean ridges on either

sides show a series of stripes of Normal and Reverse polarity. The scientists were further

surprised to discover the ages and widths of the stripes, matching from one side of the ridges to

the other.

Data from ocean topography (ridges, trenches, & faults), ages of ocean rocks and

sediments together with paleomagnetic results led H.H. Hess of Princeton University to suggest

that the Sea floor is spreading. According to the hypothesis of sea floor spreading, lavas form

ocean ridges are extruded and flows laterally, forming a new crust that move away slowly from

the spreading center. One consideration that led scientists to the development of a new concept

is that oceans cannot go on increasing their area and their old crust must be consumed in the

Earth’s interior at the same rate as it is added from the MOR. It was suggested that with the

formation of new crust at MOR, the old crust is destroyed at deep-sea trenches. In this process

the continents were also drifted riding over the moving ocean floor. In 1968, three scientists, B.

Isacs, J. Oliver and L.R Sykes, at Lamont Geological Observatory published a significant review

of all the data and advanced a theory that continents along with their rigid upper mantle part (i.e.

lithosphere) move as enormous slabs, later called tectonic plates or lithospheric plates. This

concept developed into what is familiarly called plate tectonics.

3.2 Plate boundaries

There are about 12 lithospheric plates, demarcated by trench, ridge, or faults.

Accordingly there are three types of plate boundaries. Each type of boundary has certain

geologic characteristic and processes associated with it.

Divergent boundaries are those along which plates separate. These boundaries are

characterized by active basaltic volcanism, shallow focus earthquakes and high rates of heat

flow, as at Mid Oceanic Ridges. The outpouring of magma along ocean ridges and building of

the oceanic lithosphere is volumetrically the most significant form of volcanism.

Convergent boundaries are the locations where the leading edge of one plate overrides

another plate. The overridden plate is subducted along the trench and resorbed by the deep

mantle. It is at the convergent boundary that we have mountain or fold belt. Only at this

boundary we have deep-focus earthquakes.

The third type of margin is the transform fault. Here the plates slide past each other,

without creating or destruction of plates. Transform faults are characterized by shallow-focus

earthquake with horizontal slip. Each plate is bounded by some combinations of these three

kinds of boundaries.

3.2.1 Plate tectonics theory

The plate tectonics became a global tectonics theory, conforming to all observations

made on continents and oceans. All earth science research is now viewed and assessed in light of

this theory, be it mountain building, assembly and dispersal of continents, resources,

paleoenvironment, or paleomagnetism.

Fossil magnetism in older rocks from different continents was studied. For many old

rocks the fossil magnetic pole did not coincide with the present magnetic pole. This means that

either the rock or its continental host have moved since the rock was formed or the magnetic pole

has moved, or both have moved. For a given continent, by measuring the ages and fossil

magnetic poles for many rocks, the relative positions of continent and magnetic pole as a

function of time is shown what is called a path of apparent polar wandering. From the

understanding that the magnetic pole position has remained close to the Earth’s rotation axis, it

was interpreted that the continent has moved relative to the pole. The paths of polar wandering

give information about the N-S movement and rotation of the continents. The Deccan Plateau

lava flows has age of 65 million years. The record of fossil magnetization in these lavas

suggested that at this Geological time India was located near latitude 45o S as against its present

position in northern hemisphere. Calculation gave that India moved with a velocity of 5cm/ year

until it crossed the equator about 50 million years ago before colliding with Asia and forming the

Himalayan Mountain.

The continent of Antarctic, once in the assembly of the Gondwanaland, is all covered by

ice. It is therefore called the cryo-continent. For about 50 million years this continent separated

from the continents of Pangaea and is now located in the South Pole. Antarctic remains dark for

6 months because the Sun never gets far above the Antarctic horizon in the months of May to

October. The Antarctic runs for about 4000 m above sea level. It is for this reason also that it is

even colder. In winter, the area of this ice continent nearly doubles because of frozen ocean

water. Therefore, men did not enter Antarctic, although explorers made expeditions in the Arctic

long ago. Due to the ice cover, the Sunlight is reflected away and the reflectivity (or Aledo) is up

to 0.85, against the Earth’s albino of 0.37. Hence, the Antarctic has an average temperature of -

49oC. However, the surrounding islands and coastal regions are less severe cold.

From aerial photographs, Antarctic is divisible into two parts, Western and Eastern

Antarctic, along the West Greenwich meridian. The East Antarctic is the main art of the ice

continent where we find Precambrian rocks similar to the shield areas. The rocks show at the

surface due to high topography. The Western Antarctic extends as a peninsula toward South

America, appearing as if it is an extension of the Andean Mountain.

Antarctic is the locus of the south geomagnetic pole, besides being a major reflector of

Sun energy. It is also not having human activities. Antarctic therefore offers a full-scale

experimental model for the geophysicist, climatologist, geologist and meteorologist. About 12

nations showed interest and a treaty of 1959, suspending national claims to Antarctic territory,

encouraged countries to have their permanent stations on Antarctic.

Since Antarctic thick ice is very old in the basal part, it definitely preserved an invaluable

record of the Earth’s past climate. Ice cores drilled in Antarctic by Russian scientists have

produced climatic record of 200,000 years or more. India has also a station Gangotri and is doing

biological, atmospheric and geophysical-geological researches. . Countries are trying to grab

Antarctic land for no obvious reasons. You can also go to Antarctica as there are no visa

requirements and on your return journey think of towing away an Antarctic iceberg in case of

water scarcity back home. There are a number of icebergs in the surrounding ocean of Antarctic.

An iceberg is like a mountain floating in less dense water. About 90% of these icy mountains are

below water because ice is about 10% less dense than water. And you know from Archimedes

principles (a body in water is pushed upward by a force equal to the weight of the water) that ice

is about 10% less dense than water. So when 90% of the ice is under water, the floating iceberg

is with almost 10% of its mass above the surface. Some icebergs when they are huge get broken

off seaward end of the glacier, while others are formed when ice sheets break loose.

Glacier formations have been at many times in the Earth’s history. There are three major

glaciations before the Pleistocene: One at 3 billion years (Arching age), second at 2.4 billion

years (Early Proterozoic), and third glacier at about 300 million years (Permo-Carboniferous).

The last glacier was at 1.8 million years ago. Glaciation is evidenced by U-shaped valleys, roche

moutanees (polished rocks by passing glaciers), moraines (erratic rock pieces dumped by

glaciers) and drumlins (heaps of material like ancient burial mounds laid parallel to the

movement of glacier) and eskers (long ridges of material laid down by treating glaciers). Older

glaciers are recognized only by tilites and oxygen isotopes studies. Various theories have been

advanced for the occurrence of glaciations, amongst them fluctuations in Earth’s orbit, changes

in rotation axis of the Earth (Milankovich cycles). Ice ages have cycle of about 100,000 years

and less than 20, 000 years of warm period (interglacial period). The last ice age ended at about

10,000 years ago. The warmer period since then is known as Holocene. Archeologists suggest

that it was during glacial periods that humans migrated across the world. When ice turned into

ice humans crossed between Asia and Alaska to reach America via Bering Strait.

3.3 Hydrogeological cycle

The watery and icy regions are connected by a water cycle, technically called

hydrological cycle. This becomes obvious when we look at the constant evaporation of ocean

water whereby air takes the water vapour with it, forming clouds that shower on the surface

either as rain or snow. About 78% precipitation occurs over the oceans, making a simple water

cycle---water evaporates, rises, forms clouds which condense and rain again on the ocean.

The water cycle becomes complex when rain or snow falls on land. On the land, the

water is carried in a river and returned back to sea. The river or stream water flowing on the land

is called runoff. Runoff water is also formed when large quantities of snow melt in spring and

summer months. When the runoff water from the two sources becomes large, the rivers swell and

can lead to flooding, as we find every year in the river Brahmaputra in northeastern India.

Warning about floods is given by meteorological department on the basis of weather conditions

and continuous record of water levels in each stream so that people can go to safe places in

advance of flood.

Blockade of the river water by sediments or from landslides form lakes which often

become sources of fresh water. Lakes are formed when river water finds low-lying areas on their

route.

If the rain water is absorbed into soil and trickles into the ground where it soaks into pore

spaces of sandstones and other sediments it becomes the groundwater. If the pores of the

subsurface rocks are completely filled, we have the zone of saturation. The upper boundary of

the zone of saturation is the water table. Materials above the water table are moist and form the

zone of aeration in which air occupies much of the pores. Ground water that flows though

permeable sediment and rock is called aquifer. The aquifer, as a stored underground reservoir, is

available to humans either as springs or in wells. The storage of groundwater is always in the

pore spaces and fractures in rocks and unconsolidated sediments.

Wells are dug or drilled to reach an aquifer. The level of water in the wells is the same as

the level of surrounding water table. As stated above, this surface is the boundary between two

zones of rock or soil. The one below the water table is saturated zone where pores are completely

filled. Below this is the impermeable layer which acts like a barrier for the groundwater. The

groundwater table lies at varying depths beneath the surface, depending on topography, nature of

rocks that retain water etc.

When water is drawn out of a well, it is replaced by surrounding water in the aquifer.

Over pumping of the well lowers the local water level (called drawdown aquifer) and results in a

cone of depression around the well. Water from rain replenishes the water content in an aquifer

and is called recharge. However, if withdrawal of groundwater is more than the recharge rate,

the well becomes dry. If recharge area is at a higher elevation than rest of the aquifers, we have a

sloping water table. In this situation the aquifer contains the water under pressure because the

water at the top of slope exerts gravitational force on the water down slope. In a well dug in this

aquifer, water spurts above the land surface in the form of a fountain called artesian well, name

after French province Artois where such well were first drilled.

Fresh water is Earth’s most precious natural resource because it is essential for life. Fresh

water availability depends on several factors such as amount of rain, infiltration, porosity and

permeability of subsurface rock or sediments, and recharge. Human activities can change these

factors, especially by overuse and causing pollution of recharge areas by sewage, industrial

wasters, chemicals or pesticide etc. The pollutants spread rapidly through permeable aquifers,

contaminating the ground water and making it unsuitable or hazardous to drink. Humans must be

aware of how their activities affect the ground water system. To discover groundwater and its

monitoring is the job of a groundwater scientist, called hydrologist. He estimates the direction of

groundwater flow with the help of topographic map, thus helping farmers and town planners in

locating new wells in their area. One must study the water in his area to know where water is

located and whether it is fresh or salty and how is this water is obtained. Water containing high

concentration of calcium, magnesium or iron is hard water which is obviously less favored as

compared to sweet water. In the developed world, the hydrological cycle is rarely seen working

in its natural form. People make dams and flood-control systems to store water and generate

electricity to the needy population.

Chapter 4

Atmosphere, our Airy Earth

4.1 Atmosphere is an envelope of gases

In preceding two chapters we talked about geosphere and hydrosphere. Now we have

another sphere called Atmosphere. It is a gas envelope that surrounds the Earth, without which

no life could exist or survive because it contains oxygen which is essential for life. According to

scientists, the atmosphere is mainly composed of 78% nitrogen (N2) and 21% oxygen (O2) and

the remaining 1% consists of an inert gas argon (Ar), carbon dioxide (CO2), methane (CH4) and

water vapour (H2O). The Earth’s atmosphere also contains tiny solid particles such as dust, salt,

& ice and airborne micro-organisms such as fungi and bacteria whereby we get airborne diseases

like flue. Today, oxygen and nitrogen are continually being recycled between atmosphere, living

organisms, the ocean and Earth’s crust, emphasizing once again a close link between geosphere,

hydrosphere, biosphere and atmosphere. You may wonder why nitrogen is the most abundant

element in the atmosphere. The reasons are: it is unreactive to materials that make up the solid

Earth; it is very stable in the presence of solar radiation having no chemical reactions occurring

there; it is involved with oxygen in the life cycle of living biosphere and fossil organic matter

since geological time; it has limited solubility, like oxygen, in ocean water. These are also the

reasons for the fairly constant amount of N2 and O2 in the atmosphere over several years. The

concentration of CO2 and water vapour is in parts per million. Concentration means the number

of molecules within the same volume. It is convenient to talk about proportions of gases, e.g. O2

= 21% of the molecules of gas in the atmosphere. The CO2 is 0.39% which can be expressed in

mnemonic way by saying 390 parts per million or ppm. This number is called mixing ratio. The

CO2, water vapour (H2O) and methane (CH4) play an important role in regulating temperatures of

the Earth. Water vapour, methane and CO2 in the atmosphere are therefore called greenhouse

gases that keep the Earth warm by absorbing heat radiated by the Earth and preventing the heat

from escaping into the outer space, similar to a greenhouse. CO2 is also cycled between the four

spheres, stated above. Water vapour varies between 4% to nearly zero from place to place and

CO2 is also variable from the present value of 0.339 % (or 339 ppm) to 0.38% (or 380 ppm, this

year slightly more) of the atmosphere. Unlike symmetrical molecules of N2 and O2 which are

made up of two identical atoms, whose electrical fields cancel each other out, the greenhouse

gases have more than one chemical bond one or more of which interact with IR light in the

atmosphere, holding thermal energy and thus becoming greenhouse gases.

The Earth’s atmosphere in the geological past is found to change considerably. Scientists

think that the atmosphere began to form at the same time as the Earth’s geosphere began to form.

The early atmosphere probably contained helium (He), hydrogen (H), methane (CH4), ammonia

(NH3), carbon dioxide (CO2), but without oxygen. This was the time asteroids and meteorites

began to collide with the Earth. At this time the Earth had not acquired sufficient gravity. Hence

most of the light gases, like H, and He, escaped into space. But once the Earth began to

differentiate, large quantities of gases, especially CO2, SO2, NO2, N2O, CH4, NH3, were emitted

from volcanic eruption but this early atmosphere had no free oxygen from the beginning. The

most probable source of oxygen was dissociation of water molecules (in the ocean) by UV rays

from the Sun. The reaction, 2H2O = 2H2 + O2, is called photochemical dissociation. Another

source of oxygen is photosynthesis brought about very early, about 3.5 Ga, by a single-celled

algal organism called Cyanobacteria in the ocean. This is photosynthesis reaction: H2O + CO2

+ Sunlight = organic compound CH2O + O2. Over a period of a billion year or so the cumulative

effect of these early one-celled, photosynthesizing organisms was to transform Earth’s

atmosphere by removing huge amount of CO2 from the atmosphere and generating free oxygen.

When photosynthesizing organisms died, they sank to the bottom of the ocean and were buried.

Their organic molecules, which they produced and which composed of their tissues, were

incorporated in the sediments. These lithified algae appeared as a fossil called stromatolytes in

marine sediments of Late Archean (3.5 Ga) in Western Australia and in Early Proterozoic

elsewhere, suggesting that early oceans were full of algal mats to produce more oxygen. That

oxygen was liberated by Cyanobacteria is evidenced by the occurrence of banded iron formation,

familiarly known as BIF. Scientists know that when O2 in atmosphere and in dissolved water of

the ocean reacts with the reduced iron (Fe2+

) occurring in the minerals (magnetite Fe3O4, wustite

FeO, fayalite Fe2SiO4, pyroxene Fe2SiO3) of the mafic melts produced from mantle, it forms

ferric oxide, seen as red colour on the rocks and weathered soil. The BIF, containing alternate

bands of chert (silica) and iron oxide, is the proof that the oxygen was liberated by

Cyanobacteria and was dissolved in the ocean. Remember that no more than 1% oxygen can be

dissolved in ocean water which already has oxygen in its H2O. When the dissolved iron was used

in chemical reaction, oxygen began to increase in atmosphere. Thus, Earth’s atmosphere

gradually evolved to support more complex life on land and sea. Later, higher plants supplied the

rest of the oxygen to have the present level of 21% in the atmosphere. Oxygen is most stable

form in molecular oxygen (i. e. O2). As O2 accumulated in Earth’s atmosphere, an ozone layer is

formed (O2 + O = O3), providing an environment where new life forms could develop.

Remember that Ozone is a less stable molecule with three oxygen atoms (O3). Ozone forms in

the air after thunderstorm. It is a component of smog. Ozone is reactive and toxic to lungs. The

ozone is found in the upper atmosphere and protects us against UV rays from the Sun because

long exposures to UV rays cause skin cancer and other diseases. We observe Ozone Day on 15

September every year.

4.1.1 Atmospheric pressure

You must know that the atmospheric gases are pressing you with a weight equivalent to a

10 m column of water. But you do not feel this weight crushing against our bodies because the

pressure inside our bodies equals that of the surrounding air; there is thus no net force for us to

feel. Another way to think about the atmospheric pressure is to measure the height of mercury

filled in a glass tube of one square centimeter cross section and about 1 meter high and placed

with its open end in a reservoir of this metal (Hg) exposed to the air. We observe that the

mercury in the tube stands at 76 cm height as it is balanced by the atmospheric pressure exerted

on the reservoir. If we do this experiment at sea level, using water, instead of mercury, in a glass

tube of 1 cm cross section and slightly more than10 meter high, we will see that water in the tube

stays at about 10 meter high. This means that the air at sea level exerts about as much pressure as

a 10 m column of water. We can, therefore, make a water barometer but we need a spacious

house to display it. Since mercury is denser liquid we use mercury barometer to have sensitive

size. The mercury barometer is also used by doctors to measure blood pressure of his patients. In

houses we have a no-liquid barometer, called aneroid barometer which contain very thin-walled

metal box which expands or contracts, according to the fall or rise of the atmospheric pressure.

The pressure at sea level is designated as 1 atmosphere pressure. Pressure by definition is

Force per unit area. So the SI unit for P is N/m2 which is equivalent to 100,000 pascals (10

5 Pa),

in honour of the famous mathematician Pascal. In view of our experiment with the glass tube in

mercury, we can calculate atmospheric pressure by using the formula, dhg where d = density of

mercury, 13.6 g/cm3; h = height 76 cm of mercury, and g = acceleration due to gravity, 9.8

cm/s2. This gives 101292.8 pascal or 101292.8 kg/m/s

2 as an equivalent unit. This given value

of 1.01292x105

Pa is equal to 1 bar (in old C.G.S system of units (1 bar = 106 dyne cm

-2). Thus,

1 bar is nearly equal to one atmosphere pressure in the given SI Units. In brief, 1 atm P = 1.013

bar (rounded). At sea level the atmospheric pressure in SI units is equal to 100,000N/m2, or 1000

millibar (mb).

Atmospheric pressure varies at a particular time and place. The differences in pressure

are very small, hence we use millibars, thousandth of bar (1 millibar = 1/1000 bar) to measure

atmospheric pressure. The pressure variation is mainly by heat of the Sun. We know that hot air

expands and becomes less dense. Measurements have shown that 1 cubic meter of air at 20oC at

sea level has a mass of 1.2 kg, while at a height of 10 km the same volume of air has mass of 0.4

kg. This clearly shows that higher you go above the sea level, the lower would be the air

pressure. On the Everest mountaineers record 350 millibars, about one-third of that pressure at

sea level. It means at such high altitude it is hard to get enough oxygen and artificial oxygen is

essential to survive on the summit of Everest. Oxygen in our blood stream is used to form

Oxyhemoglobin, a chemical used by human organs. In addition to being at low pressure, the air

at high altitude also has less water vapour. It is for this reason that people in high places are

likely to dehydrate faster. But people living in high altitude such those living in Tibet, in High

Himalaya, in Andes, have adapted to their physiology, having high blood flow, bigger lungs than

those living near sea-levels.

4.1.2 Atmospheric layers

Like the solid Earth, the atmosphere is also divided into distinct layers. We have 5 layers

as we go high. These are: troposphere, stratosphere, mesosphere, thermosphere, and exosphere,

each unique in composition and temperature. Troposphere is the layer closest to the Earth’s

surface. It contains most of the mass of the atmosphere. Its thickness varies with location, in a

similar way as the crust below our feet. Near the equator the troposphere is about 16 km deep

and at the poles it only 8 or 9 km thick. Although thin, the troposphere has the weight of the rest

of the atmospheric layers that press it down. Troposphere contains 75% mass of the atmosphere

and therefore it becomes the prime layer for having most activities related to weather, as will be

discussed later.

The average temperature at the Earth’s surface is about 14.5oC, although exact

temperature depends on whether we live in India or Norway. When you measure T through

troposphere, we find an interesting phenomenon. As you go up, T drops with height. Finally we

reach a point where T stops decreasing. We have minus 50oC (-50

oC) at this point and we call

the location by the name tropopause. The reason for the drop is that the atmosphere does not

absorb huge amount of incoming solar energy.

Weather occurs primarily in the troposphere because it contains all the gases.

Commercial jets for example generally fly just above the troposphere in order to avoid

turbulence caused by weather disturbances.

Beyond the troposphere we arrive at a layer called the stratosphere. Here, the T starts to

increase again and goes on climbing until it has reached near 0oC at the top of stratosphere. The

reason is that something is heating up from energy. This energy is coming from the famous

―Ozone layer‖ within the stratosphere. The ozone layer absorbs most of the UV radiation in solar

energy, warming the stratosphere. The ozone layer protects us from the worst effects of the UV

rays from the Sun in form of skin diseases. Ozone layer above Antarctic is found to have a hole,

discovered by a team of British Antarctic Survey. The hole is attributed to the

chlorofluorocarbon (CFC)---inert gas molecules used in cooling for refrigerators and in

propelling deodorants from spray can etc. Once in atmosphere, the CFC stays for many years (80

-120 years). CFC decomposes from the effects of solar energy during which a series of reactions

generates Cl2 which react with ozone and depletes this zone. Estimates are that one Cl atom can

destroy at least 100,000 ozone molecules in one or two years before it forms HCl and carried

away by atmosphere. It is for this reason that we do not use CFC any more.

Stratosphere contains only 25% of the atmosphere but there is water vapour in it. Hence

stratosphere is almost devoid of clouds. Stratosphere extends about 50 km above the sea level

beyond which a limit comes when T touches 0oC. This point is called stratopause.

Above the stratopause is the mesosphere. Here the temperature is down, although some

solar energy is still being absorbed. Top of the mesosphere shows temperature around -90oC and

defines mesopause at about 85 km above sea level. At this height we have little water which

appears in night-shining clouds, called ―noctlucent‖ which are made of ice crystals. These clouds

are seen only at night in polar regions.

Troposphere and tropopause are termed the lower atmosphere by meteorologists, whereas

the stratosphere and mesosphere are middle atmosphere. The upper atmosphere consists of one

layer called thermosphere. The thermosphere and upper mesosphere are ion-rich regions and

can be called ionosphere. Here, the ions are produced by the interactions of high frequency solar

radiation with atoms of atmospheric gases. Incoming solar rays strip electron from N2 and O2

atoms. As result, the ions cast a faint glow. The glow near the Earth’s magnetic poles gives fiery

light called auroras. Thus there are no molecules in thermosphere. The thermosphere is regarded

as the start of outer space. It is this region where space shuttle and crewed space ship fly, besides

satellites, because there is no friction as a result of the absence of air.

The thermosphere ends up at about 600 km at which exosphere starts. This is a layer of

hydrogen (H) and helium (He) atoms from the solar wind that gradually fades away into outer

space. Exosphere is the outermost layer of Earth’s atmosphere. It extends from about 600 km to

more than 10,000 km above the Earth’s surface. There is no clear boundary at the top of

exosphere. It can be thought of as a transition between Earth’s atmosphere and outer space.

4.2 Weather machine

Circulation of the atmosphere contributes to weather, because the atmosphere is the most

restless component of the Earth. Meteorologists or scientists studying weather have recorded

wind speed up to 300 km per hour. This is a big contrast to the movement of ocean currents

which is a few km an hour and of continental movement which is about 5 cm a year. Weather

pattern shows that the general circulation of the wind is E-W or N-S, because the direction of

Earth’s wind is influenced by Earth’s rotation---Coriolis effect. As a result of the Coriolis effect

the rotating Earth from W to E results eastward movement of air on the equator and in the

northern hemisphere, at a speed of 1670 km/hour. The air moving toward the poles appears to

curve to the right or East. The opposite is true for air moving from poles to the equator because

the eastward speed of polar air is slower than the E-ward speed of the land over which it is

moving. Remember that a wind gets its name from the direction it comes, and not where it is

going. For example, 30km/hr NW wind indicates that wind is blowing from NW at a speed of

30km per hour.

The movement of the atmosphere is primarily due to movement of air molecules from

high pressure region to low pressure region. The air near the Earth’s surface is heated. As a result

it expands and becomes less dense than the surrounding air. This warm air rises. At higher

altitudes this rising air cools and its density increases. Therefore it sinks relative to the

surrounding air. As it sinks, it warms again, and the process repeats. This process develops

convection currents, resulting into transfer of thermal energy in the atmosphere. Thermal energy

in the atmospheric gases is due to solar radiation and is in form of heat from the Sun. Most of the

solar radiation or solar energy that reaches the Earth’s surface is in the form of visible light and

infrared waves. About 30% of solar radiation is reflected into space by Earth’s surface,

atmosphere or clouds. Another 20% is absorbed by the atmosphere and clouds. Thus, about 50%

of the solar radiation is absorbed by the Earth’s surface and keeps the Earth warm, as stated

already. Thermal energy in the atmosphere is transferred by convection---movement of heated

gas molecules and atoms from one place to another in the atmosphere. This can be appreciated

when we see the places on the Earth where the Sun rays are striking straight over 12 months

period, These are the Tropic of Cancer in the Northern hemisphere from where the Sun moves to

Equator and then down onto the Tropic of Capricorn on the Southern hemisphere. The

redistribution of thermal energy in form of heat/light over the period of 12 months drives the

season about which we have already discussed in chapter 1.

Uneven heating of Earth’s surface is the cause of air-pressure differences and thus

movements of the wind. The air-pressure differences or in other words density differences drive

the Earth’s weather. Strictly speaking, it is not only the temperature but there are other elements

that affect weather. These are wind, precipitation, cloudiness and humidity. The general pattern

of weather that occurs in a region of a period of years is what we call climate.

Besides Solar radiation, the second source of energy for the movement of atmosphere is

due to the effect of rotation of the Earth itself. We know that the Earth spins from W to E.

Everything on the Equator moves at nearly 1700 km/hr (more precisely 1670 km/hr) to have a

complete rotation or one lap per day. But as we go near the Poles, the rotational velocity will be

slower and at the poles the velocity is almost zero. So if we launch a rocket from the North pole

straight at London, it would never arrive because it would have no rotational velocity. This is

like throwing a ball by a man on the merry-go-round towards a man standing away, who will

always miss it by a small distance. The Earth’s rotation would have shifted London out of the

way before the rocket reached there. If we view the situation from the ground, we observe that

the missile would appear to be deflected to the W by a force which we call Coriolis force, in

honour of Gustav-Gaspard Coriolis who wrote the equation for this phenomenon in 1835.

Anyone planning an intercontinental missile attack takes this phenomenon into consideration.

The implication of the Coriolis force is that Equator-bound objects coming from the N or

S are pushed toward the W. On the other hand, object moving away from the Equator are

diverted E.

We will now consider how these two factors, namely solar radiation and Coriolis force,

control or affect the weather. Remember that the weather is a global system and does not begin at

any place. But to make things simpler, we assume that it starts at the Equator. The solar radiation

(heat energy) on the Earth is more on the Equator than at higher latitudes. Consequently, the air

gets hot at the Equator and expands to attain a low density. So it starts to rise. As the hot air

moves upward, it is replaced by humid air from oceans. The moist air thus creates a zone of

lower pressure by clouds, precipitating large rains along the Equator. This is why the Equatorial

regions are among the Earth’s wettest regions, and are home to the great jungles of Africa and

South America. Here, rain fall is generally 150 cm per year. Since the two air masses, one from

land and the other from ocean converge, the Equatorial region is known as the convergence zone.

This zone is almost without wind because the hot air moved straight up. This created a problem

for the ships for want of wind. The ships stuck at the equator for weeks in the ―doldrums‖ – now

a proverbial word for situations not allowing taking a decision.

When the rising air eventually reaches the troposphere, it can rise no higher and spreads

laterally toward the Poles. This is now a dry air which spreads and, being cold, it becomes

denser. Hence it sinks down toward surface at latitudes of about 30o N and 30

o S of the Equator.

The sinking, dense air produces areas of high pressure with drier conditions. This dry air

(without water) piles up and produces desert areas, for example Sahara desert of North Africa,

The Great Victoria desert of Australia and the Sonoran desert of Arizona and Mexico. All these

dry areas are about 20 -30o

N or S of the Equator. Some of the sinking air moves from the high

pressure zones back toward the Equator. As it flows, it produces the prevailing winds. But

immediately to the N and S of the Equator the winds, called Trade Winds, blow from NE above

the Equator and SE below the Equator. This is because the winds (Trade winds) are dragged

from N to NE by Coriolis force in the Northern hemisphere; and from S to SE direction in the

southern hemisphere. These winds got their name, Trade Winds, because they were extremely

useful for the people planning maritime commerce. The pair of convection cells between 0 and

30o N and S, which produce the prevailing winds, are called Hadley Cells where one finds the

world’s great deserts stated above. Although most of the air that sinks at 30o N and S latitude

returns to the Equator, some of this moves towards Poles. Somewhere around 60o

N and S

latitude, this low-altitude air flowing from the Equator meets the cold air coming from the Poles.

As the air descends, it creates a high pressure zone from which the Trade Winds head for the

Equator. But the rest of the descending air heads toward the poles. Here the warmer air moving

away from the low latitude is buoyed upward by the cold polar air. The descending air rises and

moves back toward 60o N and S. As the air sinks it completes the polar convection cells called

Farrel Cells which are the signs for westerly winds in northern hemisphere and easterly winds in

the southern hemisphere. The winds of the Farrel Cells are gentler than those involved in the

Equatorial Hadley system.

It is indeed interesting that the air flow to the N and S poles is not continuous. The reason

is that the Polar Regions have their own set of air-flow cells, doing more or less reverse to that of

the Hadley cells. The polar cells, between 60o and Pole, form because of sinking of the cold air.

Since this air is dry and hence snow has built on the N and S poles for many years. This

descending air at or near the poles has almost no rotational velocity. So it is deflected to W as it

moves away from the Polar regions. This effect enabled the sailors to discover America.

The difference in temperature between air in the Polar Cells and that in the Farrel Cells

produces one of the atmospheric most spectacular phenomena called the Jet Stream. Jet stream

is found 10 km above sea level. They are high speed winds (95 to 195 km per hour) blowing W

to E under the influence of Coriolis force. The Jet stream not only plays an essential role in

global transfer of thermal energy from equator to the poles but serves as a boon for the air travel

going faster if going eastward. The Earth Weather Machine is interesting as the Poles get 40%

energy as much as the Equator.

From the above description we understand that weather forecast is not so simple that it is

hotter in the summer and colder in the winter and somewhere in between in Spring and Autumn.

The weather is complicated by the liquid Earth below the airy Earth.

The land and sea have significant influences on the weather (and climate). When the air

blows across, it rubs against the land. Consequently, we have a ―frictional layer‖ several hundred

meters above the ground level. The rougher the surface the greater is the friction and so the

greater is the drag. Due to this rubbing effect, we can have eddies and turbulence of varying

height and width, depending on the landscape. Again, because friction reduces speed of the wind

it reduces the Coriolis effect. This causes winds in northern hemisphere to spiral out clockwise

from a high pressure region and spiral counterclockwise into a low-pressure region. In southern

sphere it is the reverse.

We also know that the entire ocean, which constitutes 70% Earth’s area, is in contact

with the air. When the air is pushed across the ocean for a few thousand km, it absorbs water,

and often it is also saturated (cannot take water any more). But this depends on T and P. When

this moist air arrives on land, especially mountain or hilly land, the air is driven uphill where P

falls and hence precipitation, as in the west coast of India, especially Kerala coast.

The different thermal properties of land and sea affect weather in a very interesting way.

We know that the land warms up more rapidly than the water when the Sun shines on it. The

reason for this is that specific heat of water is more than land. [specific heat capacity of water is

5 times more than of the rock or soil]. In the morning, when the land warms up and sea stay

comparatively cool, the air above the land gets heated faster than the air over the sea. The air

rises, causing a wind to blow from the sea to replace it. This is the land breeze. In the evening,

the land will cool faster than the sea, and the wind blows towards the shore, and we enjoy the sea

breeze.

4.3 Monsoon

Monsoon is similar to land and sea breezes. We have unequal heating of the Earth

surface. But the energy is redistributed by circulation of atmosphere and oceans. Heat generated

in tropics is transported polar ward by global circulation of air and warm ocean currents. Air

over land warms faster than that over oceans (because specific heat of ocean water is more than

any material constituting land). Consequently the hot air over land rises and creates an area of

low pressure. The low pressure attracts moist summer winds from the Indian Ocean. The two

great air masses collide against each other, giving dark clouds and rain (because of condensation

of water vapour in the moist air from oceans). When the high topography came onto existence

by the birth of Himalaya in Late Miocene when the Mt attained a critical height, the Himalaya

became a barrier to the SW flowing air currents. When the air reaches the Himadri Mountain or

the Himalaya, the air rises and it cools. Since the moisture cannot be held any more we have

rains on the Indian side—the wind-side, while the other side is a leeward side and often starve of

rain and produces deserts, like Gabi desert in Asia. The region such as Ladakh and Zanskar that

lie N of the Himalayan Mountain have only scanty rains or draught. Monsoon is linked to global

climate change. Only its strength varied since the time Himalaya came into existence. Thus, the

Himalaya also influences the climate of the Indian subcontinent by sheltering it from the cold air

masses of central Asia. But reduced monsoon intensity is linked to Sea-Surface Temperature

(SST) in the Indian Ocean because of change in the Indian Ocean Dipole (IOD) on account of

reduction in net heat input to the Indian Ocean. This reduced heat input is through the Indonesian

through-Flow of cold thermocline water from Pacific to Indian Ocean.

From above we observe that orography and coastal areas give rains. But when more

water in the air than it can hold, we get dew. Dew plays an important role in drinking water and

for agriculture. Snow is the cousin of the rain. A tiny ice crystal will form by freezing the

droplets of water. If the precipitation does not fall from the sky and only water droplets are

formed near the ground due to fall in temperature, we get fog. When denser cold air pushes the

warm air and the two with different temperature mix, then we get thunder storms and turbulence.

Extreme weather is also encountered in certain regions. The frequently encountered is the

cyclone which is a tropical storm. It is produced when a region of low pressure has inward

swirling winds around it. Anticyclones have outward flowing winds from a high-pressure zone.

Due to effect of the Coriolis force, the winds in a cyclone move anticlockwise in the Northern

hemisphere and reverse in southern hemisphere. The converging air in the cyclone is forced to

rise upward. This can result into clouds and rain with thunderstorms. Cyclones with wind speed

over 60 km per hour are called storms or hurricanes in US. In the NW Pacific they are called

typhoons.

4.4 Interaction of atmosphere and ocean

The atmosphere and the oceans are closely linked by the transfer of heat, gases and

energy from one to the other. All these exchanges are responsible for Earth’s climate and

weather. The ocean surface absorbs most of the heat from the sun and the surface currents driven

by wind move the warm water around the world and warm the atmosphere from below. The

oceans thus help to regulate the temperature of the lower part of the atmosphere. In addition,

greenhouse gases like CO2 are transferred between atmosphere and oceans. The action of winds

blowing over the ocean surface creates waves and currents. When winds are strong enough to

produce spray, tiny droplets of ocean water are thrown up into atmosphere where some

evaporate, leaving microscopic grains of salts in the air. These tiny salt particles may become

nuclei for the condensation of water vapour and form fog and clouds. The ocean, in turn, act

upon the atmosphere to influence and modify climate and weather systems. When water

evaporates, heat is removed from the ocean and stored in the atmosphere by the molecules of

water vapour. When condensation occurs, this stored heat is released to the atmosphere to

develop energy of motions in air masses. The atmosphere obtains nearly half its energy for

circulation from the condensation of evaporated ocean water.

The pattern of atmospheric circulation largely determines the pattern of ocean surface

circulation and location of clouds, which influences the locations of temperature of the ocean

surface.

One of the dramatic manifestations of the interaction between the ocean and the

atmosphere and its climate effect is the Southern Oscillation. The Southern Oscillation is a back

and forth variation of atmospheric pressure between high P system located off the west coast of

South America and a low P system located in the Western Pacific, near Indonesia and Australia.

As a result, abnormal amounts of moist, warm air cross North America, causing heavy rains and

floods in Peru while draught in Indonesia and Australia. This phenomenon is manifested by the

arrival of warm water off the coast of Peru near Christmas time, covering the cold water near

Peru. This is called El Nino in Spanish language. The El Nino cycle was first noted by the

fishermen because warm waters were less fertile and the fisheries would collapse that year. The

weak monsoon in India is attributed to El Nino effects. The world dries out during El Nino.

There is another cycle called La Nina in which there is cold water at the sea surface in the

eastern part of the Pacific Ocean near Peru. The cold water contains nutrients that allow

phytoplantkton to grow, feeding the very productive Peruvian fishery. The contrast in sea surface

temperatures between the eastern and western equatorial Pacific drives a wind along the equator

that blows from E to W. The warm water, floating on the colder water with a boundary called the

thermocline, piles up in the West. The tilted thermocline keeps the surface waters cold near Peru,

which drives winds, which keep the thermocline tilted and the cold water at the surface. The cold

water near Peru gets covered with warm water during El Nino. Although both these states (the

wind and thermocline) are self stabilizing, the atmosphere/ocean system flips back and forth

between the two climate states, about one cycle every 4 to 7 years. There is a possibility that with

global warming the Pacific may tend to favour the El Nino state, but difficult to assess the impact

on climate. Another potential feedback from the ocean to climate is called the meridional

overturning circulation in the North Atlantic Ocean. Warm water is carried to the North

Atlantic in the Gulf Stream. As the water cools, its density increases and it sinks into the abyss,

making rook at the surface for more warm water to carry heat from the tropics. The Pacific

Ocean has a surface current analogous to the Gulf Stream, called the Kuroshio Current, but

surface waters in the Pacific are not salty enough to get dense enough to sink So there is no deep

meridional overturning circulation in the Pacific.

Chapter 5

Biosphere & Earth’s Environment

5.1 The Biosphere

When astronauts and cosmonauts in orbit look homeward, they see planet Earth with four

spheres. Three spheres have been described in previous chapters. The biosphere is the youngest

sphere of incredibly thin veneer of life. The youngest entrant in the biosphere is the Homo

habilis, which appeared ca. 2 million years ago and whose brain grew until our kind—Homo

sapiens. Having powerful mind, the Homo sapiens, commonly called humans are now strong

enough to have distinct influence upon the spheres of water, air and land, so much so that

modern man has become a large-scale geological force. Man exploits the Earth resources, using

his clever technology of exploitation, which are causing environmental problems, polluting

groundwater and air, unfit to drink and unhealthy to breath.

5.2 Earth’s Environment

The Earth’s environment encompasses the terrestrial and aquatic ecosystem in which

rock (land), ocean, air and living organisms, defining lithosphere, hydrosphere, atmosphere and

biosphere respectively are interconnected by the physical, chemical and biological processes

which move the materials and energy on the Earth. Solar energy variation and volcanic eruptions

are main causes of global temperature changes in the geological past.

According to geological investigation, Earth’s climate or temperature has changed

drastically over the eons of time. Studies of rock strata reveal that for the past 3 billion years, the

Earth climate was tropical. About every 250 million years this tropical climate is interrupted by

relatively short period of glaciations which covered a larger Earth area by ice-sheets. The last

glacial epoch was 6,50,000 (6 Lac 50 thousand) years ago.

But it is also possible that volcanoes are responsible for the variations in the

Earth’s temperature or for causing climate change in that the volcanic dust, ash and gases

reduced the Sun’s radiation to as much as 30%, causing glaciations. In the current ice age of

Pleistocene period, we had four glacial periods separated by four warm interglacial periods.

There does not appear any consistent connection between periods of volcanic activity and ice

ages in the geological record. Theoretical geoscientists believe that volcanic eruptions decreased

with time because Earth’s mantle is cooling for loss of radioactivity. Modern volcanic activity on

surface is estimated to release only 130 to 230 mega tones of CO2 each year. Moreover, the

regular repetition of the ice ages at approximately 250 million years intervals suggests volcanic

eruption and other processes cannot generate a rhythmic climate variation. It is then obvious that

some sort of cycle in the Sun is responsible for the climatic variations. The world-wide fall or

rise in temperature strongly indicates a change in the heat output only by the Sun. The world-

wide fall or rise in temperature strongly indicates a change in the heat output only by the Sun.

Furthermore, the regular repetition of the ice ages at approximately 250 million years intervals

suggests some sort of cycle in the Sun. Long term T variations or climatic changes are

considered due to sun spot activity with periodicity of 11 years. Increased solar activity coincides

with warmer than-normal sea surface temperatures while periods of low solar activity coincides

with colder sea surface temperature. Note that sea surface temperature is used as an indicator of

climate. The other reasons are Milankovich cycles which occur (i) on 40.000 years periodicity

due to variable tilt of Earth axis, and (ii) on 11,000 years periodicity due to rotation of axis itself,

called precession which is like rotation of a top as it slows down its spin. If the shape of the

Earth’s elliptical orbit becomes more elliptical, the orbit elongates. As a result, Earth travels a

path closer to the Sun in some part of the year. Consequently, the temperatures become warmer

than normal. In the nearly circular orbit as it is now, the Earth is farther from the Sun and

temperatures dip below average. If the angle of the tilt of Earth’s axis decreased, there would be

less temperature contrast between summer and winter. Winters would be warmer and summers

would be more cooler. As a result, the snow in polar latitudes would not melt in summer, ensuing

glaciation. In case the Earth wobbles, the axis will rotate away from the currently pointing

toward Polaris and point toward another star called Vega, in about 11,000 years. Currently

winter occurs in N-hemisphere when the direction of tilt is as now. But by change of direction of

tilt, northern hemisphere will be tilted in the opposite direction, relative to the Sun. So the N-

hemisphere will experience summer. But these climate changes occur once in few hundred or

thousands of years. What about the existing temperature rise, which is called Global Warming.

Perhaps linking the very high temperatures with the CO2-dominant atmosphere of the

planet Venus, it was first proposed in 1861 by the noted physicist John Tyndall that temperature

variations on the Earth are due to variations in CO2. An analogy can be given from a closed car

whose glass windows permit entry of the Sun’s visible radiation, warming everything inside the

car. The window glass, like CO2, traps the heat and the inside T of the car rises. While all water

vapour in the atmosphere remains close to the ground, CO2 diffuses more energy through the

atmosphere.

5.3 Greenhouse gases

We have already stated that the Earth gets its energy mainly from the Sun. Most of the

Sun’s energy that arrives at the Earth is in the form of visible and infrared light. The potentially

harmful UV light is filtered to a large extent by the ozone layer. So the visible and infrared light

passes through the atmosphere, consisting of nitrogen (N2), oxygen (O2) and minor amounts of

CO2, H2O, CH4 and thereafter it reaches the Earth’s surface. Since the Earth’s surface is

reflective, it emits that energy. But molecules of water vapor (H2O), methane (CH4) and carbon

dioxide (CO2) in the atmosphere absorb radiation at these wave lengths because the chemical

bonds between their atoms resonate at these frequencies. Nitrogen (N2) and oxygen (O2) are

unsuitable to absorb radiation from the Earth because of their linear two-atom structure. So the

multidirectional bonded molecules of the minor gases (CO2, H2O, CH4) capture energy emitted

from the Earth’s warm surface. These gases keep the Earth fairly warm, like a greenhouse and

keep the Earth livable. Therefore these gases are called greenhouse gases. Their present amount

in ppm in the atmosphere is: CO2 = 380 ppm, CH4 = 2.0 ppm, and water vapour = 0.3 ppm (I

ppm means 1 molecule of a gas in 1000 molecules of air). The parts per million does not sound

like much but CO2 is a powerful greenhouse gas.

We know that plants use solar energy to change CO2 into carbon. Less CO2 in the

atmosphere helps to cool the planet Earth. Wind and ocean currents move heat to warm the

higher latitudes. The landscape of the solid Earth has been continually changing by its inside and

outside processes which are volcanoes, earthquakes, and plate tectonics that initiate closing and

opening of oceans, movement of continents and mountain building, all undergoing perpetual

erosion. Earth’s temperature is a balance between the rate at which the Earth absorbs energy and

the rate at which the Earth re-radiates it.

The deepest sediments show that there were at least 10 distinct temperature cycles which

coincide with high carbon dioxide (CO2) contents in them. Knowing that in the early period of

Earth’s history the source of CO2 in nature was primarily volcanic activity. Volcanoes release

CO2 into atmosphere and this CO2 is also dissolved in ocean water in order to maintain

equilibrium between atmosphere and hydrosphere. The equilibrium is also maintained with the

solid Earth by the process of weathering. Weathering of rocks consumes CO2 .For example

Feldspar + H2O + CO2 → (K,Na,Ca) cations in solution + clay + (SiO4) in solution +OH-

2Mg2SiO4 + 2H2O + CO2 → Mg3Si4O5(OH)2 + MgCO3

Olivine serpentine magnesite

Chemical weathering carries elements to the ocean. Fe is at once precipitated; much of Mg and

Na are taken up by the oceanic crust. Al is kept in clay minerals. This leaves Si, Ca as important

elements which are involved in modern biogeochemical cycles and make up the shells of diverse

organisms that form in the ocean and whose precipitation leads to chert (in the case of SIO2)

and carbonates (in case of CaCO3).

Let us take a Ca & Si constituting-mineral wollastonite (CaSiO3)

Erosion of CaSiO3 (wollastonite) by interaction with H2O and CO2 form dissolved ions of Ca 2+

and HCO3- & H2SiO4

o (neutral silicate), as per reaction:

CaSiO3 + 3 H2O + 2 CO2 = Ca 2+

+ 2 HCO3- + H4 SiO4

o

These ions percolate through soil to a nearby stream and eventually to the sea.

In the modern ocean, organisms use these constituents to manufacture their shells.

Prior to the evolution of shell-forming organisms, CaCO3 could precipitated directly from

seawater, inorganically:

Ca 2+

+ 2HCO3 → CaCO3 + CO2 + H2O

Silica can also be precipitated as opal by the reaction:

H4 SiO4o →SiO2 + 2H2O

The calcite and opal hard parts fall to the sea floor to contribute to the sediment accumulation

on the oceanic plate which on subduction gives rise to wollastonite from reaction of

CaCO3 + opal (SiO2) → CaSiO3 + CO2

The CaSiO3 is returned to the Earth and the CO2 rises to the surface in island arc volcanism.

This cycle called plate tectonic cycle is continuous and acts in controlling the CO2 in solid,

liquid and gas.

Faster erosion would trap more carbon dioxide (CO2) from the air. Consequently,

temperature would fall, permitting the young mountains to become the site for the glaciers.

When glaciations grow as a result of reduced CO2 in the Earth environment, the oceans shrink.

The smaller volume of ocean water releases CO2 in the atmosphere. As a result, CO2 becomes

more in atmosphere and the Earth temperature rises and the ice melts away. The oceans regain

the previous volume and re-absorb the CO2 they had released. Result is that a new glacial epoch

begins. If no glaciations after mountain building, it implies a balance between volcanic CO2 and

consumed CO2 in weathering. Both the atmosphere and the ocean continuously exchange CO2

with rocks and with living organisms. But when there is huge underwater volcanism as

happened about 100 million years ago when sea floor spreading was faster, the extra volume of

young hot rock on the ocean floor displaced the ocean waters so that they flooded the continents,

thereby reducing the area of the rock available for weathering. If there is excess CO2, it is added

to the ocean water. The excess CO2 in ocean water is balanced by precipitation of calcite by

chemical process given below:

H2O + CO2 = H2CO3 = HCO3 + H+

Ca2+

+ 2HCO3 → CaCO3 + 2H+ (carbonate precipitation with high p

H of ocean water)

So long as the total amount of CO2 in the atmosphere-ocean system remains unchanged, cycle of

temperature oscillations will tend to repeat itself.

The interaction and near equilibrium between the past atmosphere, ocean and lithosphere

was interrupted with the arrival of plants, about 3.5 billion years ago. The biosphere acted as a

sink of CO2 whose supplier has been the volcanic activity. Flourishing vegetation was

responsible to take up huge CO2, giving oxygen by photosynthesis. In photosynthesis the plants

and algae absorb light which (in the form of energy) is stored by a chemical called adenosine

triphosphate (ATP) in plants. The solar energy is absorbed by a pigment called chlorophyll.

This pigment absorbs most of the light, except green which is reflected and we see the plants

green. The light absorbed in day time and the energy stored in the ATP is used to turn water

(which the plants draw from roots) and CO2 (from the atmosphere) into carbohydrates/organic

compounds and release oxygen into the atmosphere. The reaction is:

H2O + CO2 +sunlight → CH2O + O2

Plants borrow several billion tons of CO2 for photosynthesis, but when plants formed coal, as in

Carboniferous Period, CO2 was withdrawn from atmosphere, causing reduction of Earth’s

temperature. That is why we had large glaciations in the following Permian Period.

When plants in poorly drained areas (called Bogs) die, they decompose. Overtime

this plant material is compressed by weight of water and sediments that accumulate. This gives

rise to the formation of peat—a light spongy material which has been used for thousands of years

by human. When peat is compressed, the next stage is lignite which is a soft, brown, low-grade

coal with approximately 1% sulphur, hence insufficient for fuel. On further compression, we get

bituminous coal and when more pressure along with elevated temperature we get anthracite

which has more than 95% carbon content.

When the dead and decaying plant organisms were buried beneath layers of clay and

mud, we get lignite oil, called crude oil. The crude oil when pumped out to surface it is used for

producing petroleum products such as gasoline, diesel fuel and kerosene. Natural gas forms

along with oil and is found beneath solid rock layers that prevent the gas to escape to the surface.

Crude oil and natural gas migrate and get accumulate in permeable (pore containing)

sedimentary rocks such as sandstones, limestones. Being less dense than water, oil and gas rise

until they reach a barrier of impermeable rocks such as slate or shale that serve as trap rock.

Geologic structures such as faults and folds can also trap petroleum. Some petroleum resources

are trapped in a fine grained rock called oil shale that contains waxy mixture of hydrocarbon

compounds, called kerogene. So kerogene is vaporized by crushing and heating oil shale and

collected as shale oil. In brief, incomplete decomposition of plants and other organic matter over

geological time gave rise to peat and other fossil fuels---coal, oil, and natural gas. These energy

sources are non-renewable because their formation occurs over thousands or millions of years.

Thus we notice that when plants flourished the exchange of CO2 occurred not only

between the atmosphere and the ocean and rocks but also with plants. In this exchange the

atmosphere and ocean gain CO2 from the volcanic activity and from the respiration and decay of

plants, whereas they lose CO2 to weathering of rocks and photosynthesis of plants. As these

processes change place, the content of CO2 in the atmosphere also changes, shifting the radiation

balance and raising or lowering the Earth’s temperature.

It also seems possible that in early geological time volcano was obviously the source of

CO2 while carbonate precipitation was the main sink of CO2, together with weathering of rocks.

And it is possible that this feedback system would have brought the cycle back to normal state.

5.4 Human and Environment

Until the beginning of the Anthropocene period, the period when man arrived on the

Earth, the Earth systems were all natural. Birds and animals have been living in a balance with

their immediate environment. We can appreciate this balance when we are told that lion, called

the king of jungle, kills only one cattle from the herd of deer or buffalo or zebra as a meal for self

and his/her own family. However, humans have an unequal capacity to modify the Earth’s

environment in which they live. Man started using the natural systems for its consumption at

faster rate and by his clever technology, influencing the planet and its four interconnected

spheres. Think how much pressure the 7 billion humans are giving to the Earth’s natural

resources. We are demanding more and more land surface, water, minerals, oils and other

resources which are likely to exhaust in a few years time from now. The present human

population of 7 billion is expected to grow for another 50 years at its current rate. With the

increasing population, demands for natural resources will also continue to increase. Whatever

humans use for their need all are derived from land resources. To extract these land resources

(Cu, Fe, Ag etc) from Earth, mining techniques disturb Earth’s surfaces, causing groundwater

pollution, and destroy quality of air we breathe. Similarly urban development is also responsible

for creating several environmental problems such as reduction of agricultural land, waste

disposal, particularly those produced by industries. Heavy metals such as lead (Pb), mercury

(Hg) and poisonous chemicals such as arsenic (As) are by products of many industrial processes.

These products pollute the groundwater, affecting human health. Again, when fossil fuels (coal,

gas, oil) are burnt for energy, gases such as CO2 and some particles are released to Earth’s

atmosphere. The global effect of this pollution is ozone depletion, global warming and acid rain.

Since 1970, ozone is found to decrease by several percent, although the total amount of

ozone in the atmosphere varies with location. Ozone layer in the stratosphere serves as a

protective shield because it filters UV radiation which is harmful to eye, skin and even crop

yields. Its main cause is the chlorofluorocarbons (CFCs) which is the result of human activity.

Ozone is low at the equator and highest in the Polar Regions. The lowest ozone amounts have

been found over Antarctic. This is called Antarctic ozone hole. Because of this decreasing

ozone an International agreement was adopted under Montreal Protocol in 1987, agreed by all

countries to phase out the production and use of CFCs and similar chemicals. Consequently

levels of chlorine, bromine and other ozone-destroying chemicals reduced in the stratosphere

since 1990. Thus, ozone depletion is ruled out as a serious cause for temperature variations of the

Earth’s surface.

5.5 Global Warming

Global warming is synonymous to Climate change but scientists prefer to use climate

change which our planet Earth is ―seeing‖ since its presence and humans experiencing it since

their appearance and especially since the time of Industrial revolution. Climate is an average of

weather over a period of some years.

Earth’s environment in a simple language is Ecology. It is a multidisciplinary field that explores

dynamics or interaction between Earth system—land, water, air and organisms (flora, fauna and

humans). Thus, Earth’s environment can be understood only by Earth system sciences which

integrates physical, biological and informatics sciences (forests, energy, mining etc.). Earth’s

Environment has not been constant since life appeared.

Realizing that Earth’s surface temperature varies from place to place, Scientists measured

temperatures over a specific time period of 100 years. These measurements show that the

average annual global temperature has increased by 0.6oC. This increase in average global

temperature is called global warming. Average temperature data came from measurements on

land and sea, historical records, particularly from ice cores, sediments cores from Lake Bottom,

and biological material such as tree rings, pollens, plant/animal fossils, insects, diatoms, and

corals. These are called proxy data to paleoclimate, since they provide a wealth of information

for past climates. Increase of greenhouse gases could increase the amount of energy that Earth

absorbs

Data from mid 19th

century until 2010 showed that the concentration of CO2 in

atmosphere has risen by the amount of 100 ppm (about 35%). The CO2 measurement was taken

at Muon Lova in Hawaii, a place far away from pollution. This is the time (post industrial

revolution) when humans began burning fossil fuels, although other factors such as solar

variations and volcanic eruptions could also cause global temperature to change.

Some scientists adopted another methodology to see if global warming is taking place in

reality. In the US, the National Climate Data Center (www.ncdc.noaa.gov) collected data to

produce average temperatures for the land, the ocean and the two combined for period from 1880

to 2010. The data indicated an average temperature rise of about 1.4oC over this period of time

for the land but somewhat less for the oceans. So, there is a debate whether global warming is

due to human-caused greenhouse gases or natural causes or both.

Computer climate models calculate the average global temperature that would result from

various changes. The best agreement with temperature data comes when greenhouse gas changes

and natural causes are used to calculate average global temperature, suggesting that natural

changes and greenhouse gas together are responsible for the observed current temperature

change. Although natural sources of CO2 (volcanic eruption, solar activity and air movements)

remained beyond human control, production of greenhouse gases by human activity (by burning

coal, oil etc.) needs to be reduced to a minimum. On this consideration the UN sponsored

agreement, called Kyoto Protocol was ratified by nearly all nations who agreed to cut the CO2

gas emission. Accordingly, nations began to change technology and lifestyle for this treaty to be

effective.

Some scientists consider that there is no global warming. They argue in a different way.

Since 70% Earth’s surface is water, so with hotter environment more sea-water turns into water

vapour which itself is a greenhouse gas. This water vapour would form clouds which in turn

reflect sun’s radiation away and thus reducing surface temperature. Non-believer in global

warming further argue that coal burning in industries produces aerosols (atmospheric clouds of

tiny particles of pollution) that would also reflect solar energy back into space. Furthermore,

some of the carbon entering the atmosphere will yield more luxuriant plant life, and also more

limestone deposits in the ocean. This means that with more CO2 production there will be

concurrent CO2 sink in plants, oceans and weathering of rocks.

Whether Global warming is entirely due to human activities or due to natural activities is

indeed difficult to resolve. Global warming is really a difficult matter to resolve. It is indeed a

complex system and does not seem to be related to specific events. Surely there would be still

cold winters and summers and a single storm can give unexpected climate fluctuations.

In 1960s, James Lovelock, a British chemist advanced an idea which he called Gaia

theory, named after Greek Goddess of Earth. According to this theory, the Earth is a self

regulating system in which living organisms regulate the climate and the chemistry of the

atmosphere in their own interest. Since billion years the amount of oxygen is maintained at 21%

in the atmosphere just in the interest of the land plants and animals. Similarly near constancy of

3.4 % salinity in ocean water is also maintained by the marine life in their own interest.

According to Lovelock, the rate of erosion of rocks would accelerate by a factor of several

hundred in the environment where life is present. According to Lovelock, this is the reason why

Earth’s atmosphere has very low concentration of CO2 as compared to that of Mars where life is

not present. Mars environment consists of mainly CO2 and N2. By contrast, Earth’s atmosphere

contains both O2 and CH4 that are produced continuously by living organisms, although the two

gases show reactions between them. Hence, by measuring the atmospheric gases, Gaia theory

enables us to know whether a planet, like our Earth has life. Lovelock thus suggests that we can

avoid huge expenditures on space probes that are meant to detect life on a planet. Lovelock

opines that the atmosphere is a complex system and is created by life.

Lovelock and his US collaborator, a noted biologist named Lynn Margulis, think that

temperature is one of the most vital parameters on the Earth to support life. Linked with

temperature is the formation of cloud which, if abundant, would reflect more solar energy back

into space. Lovelock pointed out that a chemical, called dimethyl sulphide emitted by algae

encourages cloud formation by creating aerosols of small particles on which water vapour can

condense. So the hotter the environment becomes, the more is the algae. Consequently, there

would be more clouds and hence a cooler Earth. But if the Earth cools, there are a few algae and

hence scanty clouds. The result is rising of temperature. This makes the whole system self

regulating to keep the temperature level. Lovelock argues that if there were no such adjustment

between algae and Earth’s surface temperature, mammals would not have evolved. It is in the

interest of the life that the Earth keeps balance between biotic and abiotic systems. It is the Gaia

theory which explains when ice ages start and when stop in accordance with the period when the

Earth gets too cold and when the Earth gets too hot. Lovelock’s Gaia theory however, does not

allow that we do whatever we like with the Earth’s environment. It is very risky to pump a vast

amount of greenhouse gases into the atmosphere or to remove a large part of the tropical forest.

It takes a long time to recover from any environmental damage by human or by natural

processes.

It is the unusual environment that led to mass extinctions in the geological past by natural

phenomenon and not by human who appeared very late on the Earth. The most famous mass

extinction occurred at the end of Cretaceous when dinosaurs disappeared from the Earth. This

period is also known for the extinction of fishes, and many plants and animals. Several

hypotheses were advanced for the extinction of these species. Some suggested that extinction

was due to the asteroid impact but then we must have data favouring global warming at this

period. And it is a big question as to how an asteroid/meteorite fall in Arizona could kill the

dinosaurs of Europe or far located Asia or Australia. Another theory is the volcanic eruption,

both on land and undersea, whereby enormous input of volcanic ash, gases etc. in the atmosphere

disallowed the Sun’s rays to reach the Earth. But here again we do not have climatic data to

support cooling of the Earth to support extinction by volcanic eruption. Another possible reason

for mass extinction is the plate tectonics and sudden change in shape and size of the oceans

Continents movement brought changes not only in distribution patterns of sedimentation but

altered path of ocean currents, resulting into changes of temperatures on land and near land

masses. During the ocean reshuffling, methane as a greenhouse gas may have released into

atmosphere from methane hydrate that long ago rested on the ocean floor. Billions of tons of

methane hydrate, often in the form of clathrates in ocean, remain stable in cold under pressure.

Methane is held in the molecular structure in ice crystals at oceanic depths. But a change in

ocean temperature could have liberated much methane as greenhouse gas in atmosphere, leading

to mass extinction, particularly of the Permian (250 Ma ago). But scientists need to collect data

for this hypothesis. Whatever reasons of mass extinction are, humans have to be careful to

protect their environment to keep the Earth a pollution free planet for survival of all living

organisms. Global warming has serious consequences for the living organisms as it would cause

melting of glaciers and in turn would result in sea level rise, affecting vast populations of plants

and animals with whom humans share the Earth.

If the emissions of greenhouse gases are threat to global warming, the humans can solve

the problem by adopting many useful methods and technology at individual, local or government

level. Some of these are enumerated below:

(i).Humans must use biodegradable products

(ii).Stop deforestation

(iii). Use energy efficient appliances

(iv). Manage better waste disposal methods such as composing kitchen scrap,

grow small gardens, reject plastic bags for grocery and vegetable etc.

(v). Adopt energy-efficient technology e.g. increasing vehicle fuel efficiency, install

energy efficient lights, improve efficiency of coal-fired power plants.

(vi). Adopt renewable energy and alternative energy resources other than fossil fuels, as

mentioned below.

5.6 Renewable energy

Because of the environmental pollution and global warming, humans have to adopt

alternative energy resources, mentioned below.

1. Solar energy: is freely available and does not cause pollution. Solar energy can be

used through passive solar heating, Here solar energy is trapped in materials and

slowly released for heating. Active solar heating includes collectors such as solar

panels that absorb solar energy for heating. Solar energy can be converted into

electric energy by using photovoltaic cell (briefly PVs), made up of two types of

silicon which absorb solar energy that strikes the layers. The PVs cells get their name

from the fact that photons (light) interact with the cells to flow electron to metal

plates, producing voltage. Thus solar cells directly convert solar energy to electricity.

Solar energy has greatest potential for technology breakthrough and most suitable for

countries located near Equator.

2. Hydroelectric power: Here we convert the energy of free-falling water to electricity.

It needs construction of a dam across a large river to create a reservoir. The stored

water in reservoir is allowed to flow through pipes at controlled rates and a turbine is

made to rotate to produce electricity. Scientists are also thinking of harnessing energy

associated with ocean waves.

3. Geothermal energy: This energy originates from Earth’s internal heat. The steam

produced from water heated by hot magma beneath Earth’s surface can be used to

turn turbines and generate electricity. Even hot water escaping from Earth’s interior

can also be used for geothermal energy.

4. Wind energy: is clearly a renewable energy source. Power plants are called Wind

turbines. Wind is kinetic energy. Rotation of turbine blades by blowing wind coverts

wind energy to mechanical energy which again is converted to electricity by a

generator sitting inside the hub of the structure. This conversion of wind energy into

electrical energy through wind turbines, is loosely called Windmills.

5. Nuclear energy: Here we use the energy released from nuclear fission in which atom

with heavy nucleus, e.g. Uranium divides to form smaller nuclei and one or two

neutrons. In this process a large amount of energy is released. Scientists suggest that

nuclear energy could produce electricity at much lower cost than coal and other fossil

fuels. Nuclear energy does not produce CO2 or any other greenhouse gases. But

hazards of nuclear power plants pose a great danger.

6. Biofuels: can provide renewable energy from biomass fuels such as wood, dried field

crops and fecal material from animals. If crops such as barley, wheat, sugarcane and

corn are fermented, we get Ethanol liquid which can be blended with gasoline and

can be used in cars and other vehicles. But corn for biofuels competes with food,

while sugarcane field demands large areas and thus there is a fear of forest cuts and

destruction of habitat.

Although solar energy, wind energy are pollution free and renewable, but they have

their associated problems Right now, solar power costs more than other forms of energy

because solar cells are costly and do not last forever. Also, installation costs are

appreciably high. Moreover, storage requires battery storage technology and smarter

software to enable electricity grids to cope up with this new source of energy. Wind

energy, like biofules and other renewable source, cannot be a base load energy source.

Wind turbines cannot be placed too close as they decrease wind velocity, besides

destroying wilderness area and unfriendly for aviation life and marine animals. Nuclear

energy is good for power but fear of accidents, waste storage problem and high cost of

operation is not favoured by mot nations. Nuclear proliferations and terrorist’s threat are

other reasons. Lastly, these renewable sources of energy do not contribute more 5% of all

the energy requirements.

5.7 CO2 sequestration and storage

Until such time that Nations switch on completely on the renewable energy sources,

we need to develop newer technology to reduce CO2 emission. Instead of burning the

coal in atmospheric oxygen, steam should be allowed to run over coal during coal

gasification to produce CO + H2 (coal + H2O →CO + H2). The CO is then oxidized to

CO2 and the H2 is fed to an electric-generating fuel cell (i.e. flow through a battery). Such

plants can be modified to CO2 capture. The captured CO2 could either be into a CO2-

absorbving liquid such as Ca(OH)2 or onto a chemical receptor able to capture CO2. Once

CO2 is captured then we can do one of the following:

I. Deep Storage: Since the deep ocean water hardly absorbs CO2 as it is very

slowly replaced by surface water which equilibrates with atmosphere, we can

think of pumping liquid CO2 directly into deep seat at depths more than3500

meters so that liquid CO2 would sink to the ocean floor. Because of cold

conditions and high pressure prevailing at these depths, liquid CO2 would

combine with H2O to form a solid substance called clathrate (C6H12O18),

piling up on the ocean floor.

II. Storage in Polar ice caps: Antarctica’s ice caps are underlain by hundreds of

lakes. These lakes form because of Earth’s internal heat that diffuses upward

from beneath, warming the basal ice at places. When we pump liquid CO2

through ice into the lakes, the liquid CO2 would react with lake water to form

clathrate, which would sink into the lake bottom. This process is feasible in

Polar Regions.

III. Storage in Deep sediments: In deep sediments deposited in the basins, the

pores filled with salty waters, known as brines. We can pump liquid CO2 into

these salty pores which will remain for very long time. Unlike the deep

oceans, these brines are too warm for clathrates to form and the pumped liquid

CO2 would remain in the pores without forming clathrates. As India has a

large coast line, we can think of storage in deep sea sediments for CO2

storage.

IV. Conversion to Magnesite: The ultramafic rocks (e.g. dunites) can be ground

up and mixed at high T with CO2 to form magnesite—a tough and resistant

carbonate mineral, according to the reaction:

Mg2SiO4 + CO2 = 2MgCO3 + SiO2

We can also inject CO2 into the cracks of ultramafic rocks in the mantle.

All these storage technique are not without engineering challenges &

environmental impacts.

Chemical Technology to control CO2 emissions 1. Recently Indian chemical engineers developed an industrial plant to capture the CO2

emitted from a coal boiler at Tuticorin in Tamil Nadu, India. It is a world first plant

which turned CO2 into baking powder (NaHCO3). The plant operates a coal-fired boiler.

CO2 emission from the boiler’s chimney are stripped out by a fine mist of a new patented

chemical. The stream of CO2 is then fed into the chemical plant that uses salt (NaCl) to

bond with CO2 molecules in the boiler chimney, making baking powder (NAHCO3) and

other compounds with many uses, including manufacturing of glass, detergents and

sweeteners.. The baking powder as a weak base of white colour is used in deodorizing

shoes, refrigerators etc.

The project saves 60,000 tones of CO2 emissions a year by incorporating them into the recipes of

baking soda and other chemicals.

2. Conversionb of CO2 into renewable fuel called methanol

In March 2019, Indian engineers (Breathe, P Segbastian, U. Waghmare and Rokshit Raghvan

Belur) converted CO2 to renewable fuel methanol so as to cut down the impact of greenhouse

gas emission. The research team participated in the NRG COSIA Carbon XPrize Competition

who converted CO2 into methanol according to the reaction CO2 + 4H = CH3OH (or CH4O) + O

In theory, CO2 is mingled with H, and by using some catalyst to bring about the process

economically and efficiently the process yielded methanol, used as a clean source of energy

useful for transport and to form acetic acid and formaldehyde used in industrial process.

Postscript

Until solar energy is affordable for which a breakthrough in energy storage technology is

required, India is forced to use nuclear energy, depending on the easy import of nuclear fuel. If

India, with its sufficient coal reserves and its established thermal power plants, needs to continue

its fossil fuels as the dominant energy market, it must develop further technology for reducing

CO2 emission. If fossil fuel has to continue to dominate the energy market, liquid CO2 would

have to be disposed, although it would raise the cost of fossil fuel energy in coming years. If we

shut our thermal plants out of the fear of CO2 emission, but the emission can still occur to a

notable amount from the natural burning of underground coal seams. As geoscientists, we know

that Models of estimating climate change are complex and imperfect. More than 20 climate

models have been attempted but some parameters like energy reflection and absorption by clouds

could not be incorporated. Furthermore, in nearly all climatic models estimation could not be

made as to how much ozone layer is responsible for the present global warming.

The same computer simulations that provide magnitude of the warming also suggests

that as Earth warms, rainfall will be more and even more strongly focused on tropics. It should

surprise every scientist why politicians-economists blame CO2 alone when H2O exceeds several

times as a greenhouse gas than CO2 in the atmosphere. Our planning is always short duration, 4-

5 years, to ―solve‖ any global problem due to our political system. Some countries once

supporting thermal energy reduction reverse their stand with change of regime. But the climate

change is a serious problem and requires every human and every nation to participate in

controlling the problem of global warming.

References

Gerlach, T.M. (2011). Volcanic versus anthropogenic carbon dioxide. EOS, Trans. AGU, v.92,

No.24, pp.201-202.

Gutenberg, B. (1912). Die seismische Bodenunruhe. Dissertation for Ph.D. submitted to

University of Gottingen, Germany.

Hess, H.H. (1962). History of ocean basins. In: Engel, AEJ; James, H.L. and Leonoard B.F.

(Eds.), Petrologic Studies: A volume to honour A.F. Buddington. Geol. Soc. Am. 599-

620.

Ince Martin (2007). 2007). The rough guide to The Earth. Publisher Rough guide, 304p.

Inge, Lehman (1936). Discovery of Earth’s inner core. Publ. Int. Geodesy Geophys. Union

Assoc. Seismologist, Ser A, Trav. Sci, 14, pp.87-115.

Isaac, B., Oliver, J. and Sykes, L.R. (1968). Seismology and the new global tectonics. J.

Geophys. Res. v.73, pp.5855-5899.

Lovelock, J.F. (1972). Gaia as seen through the atmosphere. Atm. Environment, v.6, pp.579-

580.

Mohorovicic, A. (1910). Das Baben vom 8, X, 1909. Jb. Meteorolog. Observatoriums in

Zagreb (Agram), fuer das Jahr 1909, v.9, part 4, Section 1, pp.1-63.

Oldham, R.D. (1989). Report on the Great Earthquake of 12 June 1897. Mem. Geol. Surv.

India, Calcutta, v.29, 379p.

Sharma, R.S. (2012). Has Earth science been ignored? Curr. Sci., v.103, Nr.3, p.256.

Sevensen, H., Planke, S. Chevallier, L., Malthe-Sorensen, A., Corfu, B. and Jamtveit, B. (2007).

Hydrothermal venting of greenhouse gases triggering Early Jurassic global warming.

Earth Planet Sci. Lett., v.261, pp.375-388.

Tyndall, J. (1861). On the absorption and radiation of heat by gases and vapours, and on the

physical connections of radiation, absorption and conduction. Phil. Mag. Ser., 4, v.22,

pp.169=194 & 273-285.

Wegener, A. (!912). Die Entstehung der Kontinente. Geol. Rdsch., v.3, pp.276-292.